Method and apparatus for generatively manufacturing a three-dimensional object

ABSTRACT

Disclosed is a method of generating a ceiling gas stream in the course of the generative manufacturing of a three-dimensional object in a process chamber by a layer-by-layer application and selective solidification of a building material within a build area arranged in the process chamber. The process chamber has a chamber wall having a process chamber ceiling lying above the build area. A ceiling gas stream of a process gas is passed through the process chamber which is streaming from the process chamber ceiling towards the build area in a controlled manner. In the course of this, the ceiling gas stream is supplied to the process chamber through ceiling inlets formed in the process chamber ceiling such that the ceiling gas stream is directed substantially perpendicularly to the build area downwards onto the build area as it exits the ceiling inlets.

TECHNICAL FIELD OF THE INVENTION

The present invention concerns a method of generatively manufacturing athree-dimensional object in a process chamber of a generativemanufacturing apparatus by a layer-by-layer application and selectivesolidification of a building material within a build area arranged inthe process chamber. In the course of this, while the object is beingmanufactured, a process gas stream is supplied to the process chamberwhich streams through the process chamber and is then discharged fromthe process chamber. The invention is also directed to an apparatusdesigned and/or controlled to preferably automatically execute such amethod as well as to a control unit designed to generate correspondingcontrol commands. The present invention particularly concerns methodsand apparatuses in which the building material is provided in powderform.

BACKGROUND OF THE INVENTION

Methods and apparatuses for generatively manufacturing three-dimensionalobjects are also known as “Additive Manufacturing” or “generativefabrication” methods and apparatuses. In the course of this, an objectis typically built up layer by layer within a build area on a verticallyadjustable building support. To this aid, a respective layer of abuilding material is applied onto the building support or, respectively,a pre-existing layer and selectively solidified in a regioncorresponding to a cross-section of the object to be manufactured. Thesesteps take place in a process chamber of the manufacturing apparatuswhich is arranged in a machine housing of the manufacturing apparatus.An example of such a method is the “selective laser sintering ormelting”, wherein the selective solidification of the building materialis effected by scanning the respective layer by a laser beam.Frequently, a manufacturing container forms a boundary frame for thebuilding material inside the process chamber by laterally confining thebuilding material on the vertically adjustable building support. In thiscase, an area bordered by the upper edge of the manufacturing containeris normally understood as a build area. In practice, the respective toplayer of the building material can often also be applied beyond the edgeof the build area thus defined; however, the building material appliedoutside of the build area does not conduce to the object manufacturingand is therefore neither selectively solidified nor subsequently loweredtogether with the building support.

Depending on the kind of the building material used, in particular whensintering or melting plastic or metal powder, undesired impurities, suchas splash, fumes, smoke, vapours and/or gases, may be generated duringthe process of selective solidification, which propagate into theprocess chamber. When a building material in powder form is used,impurities may be additionally generated by swirling up powder or powderdust in the process chamber, e.g. caused by irregularities in themetering or application process or by a local gas stream impulse onto apowder portion being too strong. Impurities can adversely affect themanufacturing process, e.g. by absorbing, scattering, or deflecting thescanning laser beam, deposit on a coupling window for the laser beam, orsettle on a building material layer, whereby disturbing inclusions canbe generated by the subsequent solidification or the application of thesuccessive layer can be impaired.

To meet high quality and efficiency requirements on the manufacturingprocess, such impurities thus need to be removed as fast as possiblefrom the process point at which it is generated. In doing so, it needsto be particularly avoided that the impurities get into a path of thesolidification radiation again and/or at another location in the processchamber. With multi-scanner-systems, in which several solidificationunits such as laser are used, there is, furthermore, a risk ofimpurities from the processing region of one laser beam getting into thepath of another laser beam and thus interfering with the process of thelatter. Besides, an increasing number of the active laser beams leads toan increasing impurity rate in the process chamber, which makes animproved removal of the impurities necessary, again.

In EP 2 862 651 A1, for instance, removal of such impurities isdescribed for a multi-scanner-machine having four irradiation units.Here, the area of a raw material carrier on which an object is built upis subdivided into four overlapping quadrants each of which isirradiated by one irradiation unit, respectively. While the object ismanufactured, it is proposed to supply fresh gas to the process chamberby means of a gas inlet ending closely above a central region of the rawmaterial carrier in a nozzle. In the course of this, the nozzle isclosed downwards in the direction to the carrier and lets the gas streamout only laterally through openings of a ring-shaped baffle plate.However, with this gas inlet configuration, impurities above the centralregion of the raw material carrier, i.e. directly under the nozzle,cannot be effectively removed.

Further, generative manufacturing apparatuses are known to the applicantwhere, for removing impurities from the process chamber, a gas stream isgenerated which vertically, centrally impinges on an upper layer of thebuilding material within a circular or an elongate, approximatelyrectangular impingement area and is laterally deflected thereby. Alsothese gas stream configurations result in problem zones of insufficientremoval of impurities in the process chamber, as illustrated in FIGS. 3and 4:

A circular impingement area A1 of the gas stream in the build area 10(FIG. 3) typically results in that, as the gas volume spreads (asindicated by arrows) along the build area 10 after the impingement, thevelocity (indicated by the respective arrow length) of the gas streamrapidly decreases with the increasing distance R from the centre Z₀ ofthe build area, this fact being caused by a rapidly (proportionally toR) increasing area of the rings marked by dashed lines, in which the gasvolume radially expands in an outward direction. This fact is made clearonce more in the figure on the left. Therefore, when a circularimpingement area A1 is small in comparison to the build area size, therapidly decreasing velocity (and density) of the gas stream does notsuffice to effectively remove impurities over long distances as far asthe edge of the build area. If a velocity of the gas stream injectedinto the process chamber is increased to such an extent that a removalof impurities over a long distance is improved, it may result in highvelocities of the gas stream directly after the impingement within thebuild area, which can lead to a detrimental blowing of the buildingmaterial.

An elongate, approximately rectangular or, alternatively, strip-shapedimpingement area A2 (FIG. 4) of the gas stream within the build area 10brings about problem zones P1, P2 of too low or non-uniformly directedremoval of impurities, the problem zones P1, P2 being formed centrallyat each long side L of the impingement area in a specific distance dtherefrom. The reason for this is, inter alia, a strong/extremecurvature at both ends E1, E2 of the strip A2. Here, the area in which agas volume of the impinging gas stream can spread in almost alldirections (as indicated by arrows) increases approximatelyproportionally to a square radius from the respective impingement pointE1, E2. This leads to considerably lower pressure conditions andvelocities in the region of the ends of the impingement area A2 than atits long sides L, where the impinging gas volume portions can flow offthe respective long side only in one direction perpendicular to thislong side directly after the impingement. As a consequence of thecorresponding higher pressure and higher velocities in these regions,gas volume portions impinging at the long sides of the impingement areaA2 drift not only to the regions having the ambient pressure, but alsotowards the two ends E1, E2 while further flowing off. Therefore,centrally at the distance d from the impingement area A2 two zones P1,P2 of lower velocities and diverging flow directions are formed. Inthese problem zones, impurities are insufficiently removed again.

In DE 198 53 947 C1, a process gas flows horizontally through a shallowprocess chamber in a channel formed by a building plane and a chambercover extending at a height of 20 cm from the building plane. Forprotecting a laser beam coupling window from impurities, it isadditionally proposed to arrange the coupling window in a chamber coverportion which is elevated specifically for this purpose. A secondprocess gas stream having a lower density is supplied into the processchamber through inlet openings arranged directly under the couplingwindow in vertical side walls of the elevated portion in a ring-shapedmanner. With this configuration, partial streams of the second processgas as well as the former gas stream partly flow at 90° to 180° againstone another. Thereby, disturbing gas turbulences or up winds may begenerated in zones of the process chamber which are not directly actedupon by the two main streams. The removal of impurities is hindered insuch zones, again.

SUMMARY OF THE INVENTION

Therefore, it is the object of the present invention to provide animproved method and an improved apparatus of the type indicated at thebeginning which can make it possible to considerably raise theeffectiveness and the completeness of the removal of disturbingimpurities generated during the selective solidification of the buildingmaterial from the process chamber. In the course of this, in particular,problem zones of insufficient removal of impurities in the processchamber known from the prior art shall be reduced.

This object is achieved by a manufacturing method of claim 1, a controlunit of claim 14, and a manufacturing apparatus of claim 15. Furtherdevelopments of the invention are provided in the dependent claims. Inthe course of this, the manufacturing apparatus and the control unit maybe further specified by the method features described herein below andprovided in the claims, and vice versa. Features of differentadvantageous further developments and embodiments can further becombined among each other.

A first aspect of the invention is a method of generativelymanufacturing a three-dimensional object in a process chamber of agenerative manufacturing apparatus by a layer-by-layer application andselective solidification of a building material within a build areaarranged in the process chamber. In the course of this, while the objectis being manufactured, a process gas is supplied to the process chamberby means of a gas supply device and is discharged from the processchamber via an outlet. The gas supply device according to the inventionis designed and/or arranged relatively to the build area and/orcontrolled such that a gas stream of the process gas streaming throughthe process chamber is shaped in such a manner that a substantiallyelongate oval impingement area of the gas stream is generated within thebuild area.

Both the term “gas stream” and the generation of the impingement areaaccording to the invention within the build area require that theprocess gas forming the gas stream streams into the process chamber at avelocity at which an inlet portion of the gas supply device can have ajet shaping effect according to the invention in an adequate manner andthe gas stream can actually stream in a controlled manner in therespective direction as far as the build area if it is not furtherdeflected as it passes through the process chamber after exiting the gassupply device. In the course of this, the above-mentioned control orsteering of the streaming behaviour of the gas stream according to theinvention is carried out by the shape-giving properties of the gassupply device according to the invention which are firstly generallydescribed above and are described in more detail below.

Therefore, in the context of the invention, an “impingement area” isunderstood as that area within the build area which is or would havebeen hit by the gas stream if, after exiting the gas supply device, itstreams or streamed in the process chamber as far as the build area in acontrolled manner without being further deflected. In cases without afurther deflection of the gas stream after it has exited the gas supplydevice, the impingement area, thus, corresponds to that region of thetop building material layer in which region the gas stream impinges ontothe layer and is laterally deflected by the layer. At the same time, asize of the impingement area may, for instance, be determined as afunction of an impact pressure generated by the gas stream within thebuild area, as will be described in more detail further below.

An actual impingement of the gas stream on the building material is notnecessarily required in the context of the invention. The methodaccording to the invention rather also comprises cases where the gasstream is partially or completely laterally deflected already beforereaching the top building material layer by further measures, such assuction caused by the outlet. In these cases, the impingement areaaccording to the invention is determined according to the abovedefinition in an abstract manner, e.g. by projecting (generally noorthogonal projection) a three-dimensionally formed gas stream shapinginlet portion (in the following short: inlet) of the gas supply deviceonto the build area. Among possible criteria of the gas stream and theresulting impingement area shaping according to the invention are thegeometry of the process-chamber-sided inlet opening area and itsorientation with respect to the build area, the geometry of an innerwall of the inlet, e.g. widening or, alternatively, narrowing and thusbundling relatively to a pipe cross-section of the process gas piping,particularly distance and ratio of a cross-section of the process gaspiping and a cross-section of the process-chamber-sided inlet opening,as well as a distance of the inlet from the build area and a velocity ofthe gas stream.

A size of the impingement area may be, for instance, determined asdepending on an impact pressure generated by the gas stream within thebuild area. Here, the term “impact pressure” is understood to mean adynamic pressure generated by the gas stream due to an accumulation ofthe stream at a solid object, e.g. a top powder layer within the buildarea. Here, during operation, an impact pressure of the gas stream atthe impingement area is typically higher than the ambient pressure inthe process chamber. If the impact pressure value measured directly atthe inlet portion of the gas supply device is set to be 100%, an impactpressure value in the region of the impingement area may amount to just50% or 30% of the initial value for a specific velocity of the gasstream since a partial volume of a non-guided gas stream may also spreadinto regions having ambient pressure which are not lying on acontinuation of its initial direction. This expanding or fraying of anon-guided gas stream over a distance may at least partially lead to apressure or velocity loss. Consequently, on the one hand, a differentdistribution of impact pressure values over the impingement area may begenerated and, on the other hand, an impingement area may berespectively differently sized and respectively differently shaped if apredetermined impact pressure value is assumed.

The impingement area being “substantially elongate oval” quite generallymeans that it is elongate and rounded. It may have a regular, e.g.elliptic, shape or, alternatively, be irregularly shaped. Concerning thegeometric shape of the impingement area, “substantially” means here andin the following that minor deviations from a specific geometric shapecaused by construction —e.g. by construction of the gas supplydevice,—are also comprised. In particular, the impingement areaaccording to the invention may represent an enveloping contour ofseveral partial areas lying quite closely to one another and, as thecase may be, overlapping with one another, i.e. it is only theenveloping contour that has the elongate oval shape according to theinvention. This may, for instance, be the case when several individualprocess-chamber-sided openings of the gas supply device lying quiteclosely to one another are provided.

Furthermore, regions of different magnitudes of impact pressure anddifferent magnitudes of impingement velocities may be present within theimpingement area according to the invention, wherein—as the case may be,locally and/or limited in time—values of an impact pressure and animpingement velocity of a partial stream of the gas stream may alsoamount to 0. This may be due to a heterogeneous jet profile of the gasstream, which may be caused by a corresponding shaping of the gas streamby the gas supply device and/or as a consequence of a deflection of thegas stream as it passes through the process chamber towards the buildarea. In the course of this, a deflection may be e.g. effected byspecific solid elements in the process chamber which at least partiallyobstruct the gas stream, for instance, a recoater used for theapplication of the building material, or by one or more further gasstreams which, for instance, impinge on the gas stream according to theinvention at an acute angle.

It is a crucial advantage of an elongate oval impingement area accordingto the invention that the problem zones of an insufficient removal ofimpurities above the build area known from the prior art as mentioned atthe outset may be considerably reduced thereby:

In contrast to an impingement area shaped as a rectangle or astraight-lined strip A2 (FIG. 4), an elongate oval impingement area A3according to the invention (FIGS. 5 to 7) possesses a non-stop curvedcontour. Thereby, great differences in the pressure and velocitydistribution of the gas stream portions at the straight sides, on theone hand, and the sharp ends of the impingement area, on the other hand,be reduced: In the middle of its curved “long sides” L0, an elongateoval impingement area A3 leads to considerably higher gas flow-offvelocities as with the straight strip/rectangle A2 (thus, theabove-mentioned two problem zones P1 and P2 of a too low ornon-uniformly directed removal of impurities are not generated) andthereby effects a considerably more effective removal of impurities incentral regions of the build area B. At the same time, the “narrowsides” L1 of the elongate oval impingement area A3, which are softer,less strongly/extremely curved when compared to a strip/rectangle A2,lead to a considerably smaller drop of pressure and velocity of the gasstream in their vicinity.

In contrast to an impingement area shaped as a circle A1 (FIG. 3), anelongate oval impingement area A3 according to the invention (FIGS. 5 to7) possesses regions having different curvature, leading to thefollowing advantageous effect:

Firstly, a “long side” L0 of the elongate oval A3 (regions of a smallercurvature) is considered in FIG. 5. The length of curved lines which,being concentric here, extend at a certain distance from an outer edgeL0 of the elongate oval impingement area A3 increases at a considerablylower rate than in the case of a circular impingement area (cf. FIG. 3)due to a comparatively small curvature. As a consequence, in this regionof the build area 10, a given gas volume impinging within theimpingement area A3 spreads (as indicated by arrows) into a considerablysmaller area (in x/y-direction) than in the case of a circularimpingement area. Therefore, in comparison, an impinging gas streamlooses only a little of velocity with the increasing distance from theimpingement area. This provides for an effective removal of impuritiesover relatively long distances.

Now, a “narrow side” L1 of the elongate oval A3 is considered in FIG. 6(regions of a stronger curvature). Here, a spreading of the impinginggas volume is considerably facilitated by the nearly circular curvatureof the edge L1 of the impingement area A3 (similarly to FIG. 3). Thevelocity of the gas stream decreases after the impingement and thesubsequent spreading in almost all directions along the build area 10 toan extent determined by the rapid expansion of the area with growingdistance from the point of the impingement. As a result, velocityrapidly drops in regions L1 of a strong curvature of the impingementarea A3.

Thus, while in the case of a circular impingement area A1 (FIG. 3) thesame conditions prevail along the entire edge of the impingement area,the elongate oval impingement area A3 (FIGS. 5-7) according to theinvention comprises regions L0 of a smaller and regions L1 of a largervelocity drop during the further spread of the gas stream impinging inthese regions. The larger velocity drop at the narrow sides L1 of theelongate oval may be compensated by arranging them close to edges BR ofthe build area 10 (FIG. 7), whereas the long sides L0 may be arrangedcomparatively far therefrom since the gas stream is capable of theeffective removal of impurities over long distances due to itsconstantly higher velocity there.

In the method according to the invention, the gas supply device maycomprise one or more process-chamber-sided inlet openings.

It may basically be arranged at an arbitrary position in the processchamber and/or at a process chamber wall suited for the gas streamshaping according to the invention.

Further, the gas supply device may basically generate several gasstreams in the process chamber. Thus, the gas stream to be shapedaccording to the invention may be a part of an entire supplied gasvolume or, alternatively, comprise the entire supplied gas volume.

The gas stream according to the invention, which generates the elongateoval impingement area within the build area, generally corresponds to amain flow direction of a gas volume supplied to the process chamber viathe gas supply device according to the invention and comprises at least70%, preferably at least 80% and as particularly preferred at least 90%of this gas volume supplied via the gas supply device. Depending on themanner and the position of shaping the gas stream according to theinvention, there may, in particular, be further partial gas streams ofthe gas volume thus supplied which have correspondingly smallerportions, are not directly guided to the build area and do not impingethere, but flow in secondary flow directions through the processchamber.

The invention is not limited to any specific build area shape. Inparticular, the build area may have a build area edge shaped regularlyor, alternatively, irregularly. However, a build area significantlyshaped as a rectangle may—particularly in combination with an elongateoval impingement area of the gas stream being aligned along a long sideof the rectangle and an outlet being preferably compatibly designed—be,inter alia, advantageous due to the constructional simplicity.

On the other hand, the geometric arrangement and design of the outletrelatively to the impingement area according to the invention canconsiderably affect the removal of impurities. In the method accordingto the invention, the outlet may comprise one or moreprocess-chamber-sided outlet openings and may basically be arranged atan arbitrary position within the process chamber or in a process chamberwall. Advantageous embodiments and arrangements will be provided furtherbelow.

In the method according to the first aspect of the invention, theelongate oval impingement area is preferably substantially axiallysymmetrical with respect to a first axis of symmetry. The first axis ofsymmetry may, for instance, coincide with a central axis of the buildarea going through a central point of the build area, being, as the casemay be, its symmetry axis. Among the advantages of an axially symmetricimpingement area, there is, beside the simplicity of the constructionalimplementation, also a correspondingly substantially symmetricaldistribution of the gas stream flowing along the build area after theimpingement. The impingement area is particularly preferablyadditionally substantially axially symmetrical with respect to a secondaxis of symmetry which is perpendicular to the first axis of symmetry.For example, the impingement area may be substantially elliptical inshape.

The gas stream according to the invention may be at least partiallyguided inside the process chamber, e.g. by a hose, a pipe etc. having anon-stop wall or having openings. However, preferably at least a portionof the gas stream streams over at least 60%, preferably at least 75%,particularly preferably at least 90% of a first process chamber heightin a controlled manner without being guided. Here, the first processchamber height is a distance between the build area and a processchamber ceiling in which the gas supply device is arranged, wherein thedistance is in a vertical direction with respect to the build area.

Herein, “non-guided” or “without being guided” means that the gas streamis not determined in its flow direction and/or spread by at least oneconstructional device, which e.g. comprises a hollow space forconveyance of process gas and is at least partially confined by aborder, i.e. comprises, for instance, a tube, a hose, a channel, anozzle, or the like. The farther the gas stream streams between theprocess chamber ceiling and the build area in a controlled mannerwithout being guided, the larger is the height ratio of the processchamber which can be freed from impurities by means of the gas stream.Besides, so much the larger portion of the process chamber may be usedfor other purposes, in particular, for the propagation of asolidification radiation, such as a laser beam.

Basically, an inlet of the gas supply device may be designed in verydifferent ways in order to achieve an elongate oval impingement areaaccording to the invention. In doing so, a process-chamber-sidedelongate oval opening area of the inlet is one possibility, it is,however, not necessarily required. With further parameters, such as, forinstance, a velocity of the injected gas stream or a three-dimensionaldesign of an inlet geometry, being suitably adjusted, the inlet of thegas supply device may rather have a polygonal, approximately rectangularor circular opening cross-section. The inlet may also have separatechannels wherein the sum of impingement areas of the partial streamsflowing therefrom to the build area results in an elongate ovalimpingement area according to the invention.

In an advantageous embodiment of the invention according to the firstaspect, the gas stream is shaped by means of an inlet of the gas supplydevice which inlet comprises a process-chamber-sided elongate ovalopening area. Thereby, an elongate oval impingement area within thebuild area is generated in a simple manner for the gas stream streamingthrough this opening area into the process chamber. Here, the openingarea of the inlet is preferably substantially axially symmetrical withrespect to a third axis of symmetry and particularly preferablyadditionally substantially axially symmetrical with respect to a fourthaxis of symmetry which is perpendicular to the third axis of symmetry.Thus, the opening area of the inlet may, for instance, be elliptical.The inlet may, in particular, represent a nozzle.

In this embodiment, the third or fourth axis of symmetry along alongitudinal extension of the opening area of the inlet is parallel to alongitudinal axis of the elongate oval impingement area of the gasstream within the build area. Preferably, an orthogonal projection ofthis third or fourth axis of symmetry onto the build area coincides withthe first or second axis of symmetry of the impingement area of the gasstream. Thus, in this configuration, the main direction of propagationof the gas stream after exiting the inlet is vertically directeddownwards towards the build area, so that a substantial portion of thegas stream reaches the build area by the shortest route.

Further, the opening area of the inlet in the above embodiment ispreferably substantially and particularly preferably entirely facing thebuild area. Thereby, it may be, in particular, ensured thatsubstantially the entire gas stream reaches the build area, namely by aroute as short as possible. Besides, the generation of zones in theregion of the impingement area in which zones a gas volume is standingor moving in an undefined or a roller-like or, respectively, vortex-likemanner, due to which a removal of impurities across the build area asfast and as long-range as possible would not be ensured, can beexceptionally effectively reduced thereby.

Alternatively or additionally thereto, here, the inlet is arranged in aprocess chamber ceiling and preferably does not or does notsubstantially protrude into the process chamber. Herein, “notsubstantially” means that the inlet does not extend from the processchamber ceiling downwards into the process chamber by more thanapproximately 10% of the first process chamber height (the verticaldistance between the process chamber ceiling and the build area). Aninlet not protruding into the process chamber may, for instance, simplybe one or more openings in the process chamber ceiling. An inlet not ornot substantially protruding into the process chamber has an advantageof not crossing any path of a solidification device, e.g. a laser.

According to an advantageous further development of the aboveembodiment, the gas stream is shaped in that an inner cross-section areaof the inlet does not increase over its extension in a directionvertical with respect to the build area towards the build area, butpreferably rather remains substantially constant. An inner cross-sectionarea which does not increase or, respectively, remains substantiallyconstant has the advantage that a flow velocity of the gas stream doesnot decrease or, respectively, remains substantially constant as itpasses through the inlet. In case of a tapering, an inner cross-sectionarea of the inlet at its process-chamber-sided opening is preferably atleast 80% of an inner cross-section area of a gas supply pipe connectingto the inlet.

Since, in the present embodiment, the inlet has a process-chamber-sidedelongate oval opening area, whereas a gas supply pipe ending in theinlet typically has a different, often a circular cross-section, the gasstream is partly being concentrated and partly being expanded or,respectively, widened with respect to the (circular) cross-section ofthe supply pipe while passing through the inlet having a constant innercross-section. In other words, inlet walls have here an expanding effecton the gas stream in its cross-sectional dimension which is parallel tothe longitudinal axis of the elongate oval opening area of the inlet(cf. FIGS. 8, 9 a-9 d).

An inlet effecting an expansion in such a manner has an importantadvantage that portions of the gas stream have an impingement anglewithin the build area which is considerably less steep thanapproximately 90°. Thereby, firstly, an impact pressure impinged on thebuilding material is reduced in these regions of the impingement areaand, secondly, an increased horizontal velocity component of theseportions of the gas stream facilitate their directed flow-off towardsthe build area edge after the deflection. This particularly affects thestrongly curved end regions of the elongate oval impingement area, inthe vicinity of which the gas stream subsequently experiences thebiggest loss of velocity. A further important advantage is a more smoothvelocity profile of the impinging gas stream than in case of an inletwithout expansion, e.g. in case of inlet inner walls extendingvertically to the build area. By a smooth velocity profile of the gasstream during and directly after the impingement within the build area,a powder blowing by the process gas is effectively prevented, whichultimately makes a higher component quality possible.

In this and other embodiments, a jet shaping of the gas stream may takeplace in a smooth or a non-smooth manner by a suitable design of aprocess-chamber-side opening and/or an inner wall of the inlet. An innercross-section of the inlet varying in a direction vertical to the buildarea may, for instance, be achieved by a suitable direction andconvexity of the inlet inner wall between the connection to a gas supplypipe (which, for instance, may be circular) and a process-chamber-sideopening (cf. FIGS. 9c-9d ). This opening may basically have an arbitrary(in the above embodiment, however, elongate oval) cross-section.

In the course of this, a convexity, curvature, or slope of the inletinner wall being designed as smooth or continuous as possible isadvantageous for the reason that too abrupt a directional change of thegas stream could cause its interruption.

In case of a stall, the gas stream would not be in contact with theinlet inner wall anymore and thus could not be guided by the latter in adefined manner anymore. This could lead to undefined process gas zonesand/or turbulences of the process gas inside the process chamber, whichshould be avoided. Therefore, in the method according to the invention,a guidance of the gas stream inside the process-chamber-sided inletportion of the gas supply device defined as well as possible ispreferably effected by a matching of the flow velocity and the inletgeometry.

According to an advantageous configuration of the above embodiment, theoutlet comprises at least one, preferably two elongate opening(s)arranged at opposite sides of the build area which opening(s) extend(s)substantially parallel to a longitudinal axis of theprocess-chamber-sided opening area of the inlet. By this arrangement,the distance travelled by the impinging gas stream after its deflectionalong the build area as far as the outlet is minimized. This is becausethe longitudinal axis of the process-chamber-sided opening area of theinlet and the longitudinal axis of the impingement area according to theinvention are parallel to each other in the present embodiment. Both theshortness and a very simple, nearly straight-lined geometry of the gasstream lines between the impingement area and the outlet in thisconfiguration (FIG. 7) contribute to an area-wide effective removal ofimpurities across the build area.

The at least one elongate outlet opening may, for instance, be a singleslit or, alternatively, comprise several slits arranged on top of eachother. These slits may, as the case may be, be provided with verticallimitations (control surfaces) for forming a pattern of a plurality ofopening areas in order to let the process gas escape through the outletor suck it in as a uniform stream and, thus, avoid a punctual orconcentrated impulse onto the process gas volume. The respective slitmay further either be end-to-end or subdivided in its length in separatesegments.

In the course of this, an orientation of the opening area(s) of theoutlet is preferably substantially vertical to the build area plane. Itis particularly preferred that two opening areas lie directly oppositeeach another at the opposite sides of the build area. A length of theoutlet or at least one of its openings may be less than a side length ofthe build area or approximately correspond to it. However, at least oneopening of the outlet preferably extends beyond that, particularlypreferably at both ends of the corresponding build area side. Thereby,in particular in configurations where a process chamber wall is at adistance from the build area edge, undesired zones, in which impuritiescould accumulate or vortices could form, can be reduced or eliminated.In addition, the outlet may also comprise further openings, forinstance, at build area sides at which the above-described opening(s) donot lie.

It further turned out that, in the method according to the invention,arranging a process chamber wall and/or the outlet at a distance from abuild area edge or a build area side, as the case may be in combinationwith an extension of the outlet beyond a side length of the build area,advantageously reduces zones in which impurities may collect or turninto undefined turbulences (cf. FIGS. 7 and 11). The distance betweenthe build area edge and the process chamber wall and/or the outlet isthen preferably at least approximately 10 cm.

In the method according to the first aspect of the invention, theelongate oval impingement area preferably lies within a central range ofthe build area covering no more than 60%, preferably no more than 20%,particularly preferably no more than 10% of a total area of the buildarea. In particular the latter, particularly preferred value “10% at themost” can be determined by an above-described, in general not orthogonalprojection of the three-dimensional inner wall geometry of the inlet ofthe gas supply device according to the invention onto the build area.

The smaller the percentage of this central region within the build area,the larger is the remaining area of the build area over which the gasstream can flow, e.g. parallel thereto, after its deflection and thuscontribute to a fast removal of impurities towards the build area edge.A central arrangement of the impingement area within the build areafurther has an advantage that the gas stream can flow off in alldirections along the build area after the impingement, so that allregions of the build area can be basically similarly purged by the gasstream. Besides, by a central arrangement of the impingement areaaccording to the invention within the build area, long routes ofrespective gas stream portions up to the build area edge are avoided incontrast to a decentralised arrangement. That way, already a singleinlet of the gas supply device generating a single central gas streammay provide for a sufficiently effective and fast removal of impuritiesfrom the process chamber even for multi-scanner-machines having severalsolidification units and a correspondingly large build area.

Such a comparatively small impingement area of a central gas streamaccording to the first aspect of the invention may furthermore lead toan advantageous synergy effect in combination with a ceiling gas streamaccording to the second aspect of the invention described further below,which is supplied to the process chamber through additional multipleceiling inlets in a direction substantially perpendicular to the buildarea. The synergy, firstly, results from substantially the samedirection of the central gas stream and the ceiling gas stream, namelysubstantially vertically towards the build area, which leads to a mutualenhancement of the purging effect according to the invention since anundesired clashing of different process gas streams can be effectivelyavoided, in comparison to the prior art. Secondly, when a central gasstream is combined with a ceiling gas stream, the respective advantagesmay prove particularly strong: While the central gas stream provides fora particularly effective removal of impurities along the build area whenan impingement area is as small as possible within the build area,impurities in process chamber volumes lying higher above, which such acentral gas stream does not directly stream through, may be effectivelyremoved by the ceiling gas stream towards the build area, where, as thecase may be, they are captured and entrained by the central gas streamflowing off across the build area towards a build area edge and are thusremoved from a region above the build area.

The proportion of the above-mentioned central region and the total areaof the build area may depend on a change of the impact pressure over thedistance between a central gas inlet into the process chamber and thebuild area. For instance, in case of a value of at least 10% of thatimpact pressure which prevails directly at the exit of the inlet throughwhich the gas stream exits the gas supply device towards the build area,the impingement area may cover approximately 5% of the build area. Incase of an impact pressure value of at least 5% of the mentioned initialvalue at the exit of the inlet, the central region may coverapproximately 20% of the build area.

In a further advantageous embodiment according to the first aspect ofthe invention, the gas supply device is designed and/or arrangedrelatively to the build area and/or controlled such that the gas streamis shaped in such a manner that several elongate oval impingement areasof partial streams of the gas stream are generated within the buildarea. With regard to at least one and preferably all of these severalelongate oval impingement areas, the whole of the above and alsosubsequent description of the invention addressing a single elongateoval impingement area of the gas stream correspondingly applies.

In this embodiment, the several elongate oval impingement areas of thepartial streams have substantially same orientation regarding theirlongitudinal extension and preferably possess a common axis of symmetrywith respect to which each of the several impingement areas is axiallysymmetrical. At the same time, it is particularly preferred that thecommon axis of symmetry of the impingement areas coincide with an axisof symmetry of the build area.

The described embodiment makes is possible to advantageously scale thefabrication concept using a few variables. For instance, stringingtogether elongate oval impingement areas, in particular with a partialoverlap, allows to extend the build area in the direction of the commonlongitudinal orientation (or, as the case may be, a common axis ofsymmetry) of the impingement areas. Without enlarging the individualimpingement area (i.e. while keeping substantially all optimisations andadvantages of an individual elongate oval impingement area for theremoval of impurities), this embodiment allows to increase the buildvolume and/or the build rates in a process chamber by a multiple. Here,in particular, an integration of further solidification units (e.g.laser and/or scanner units) for increasing the build rates of the systemis possible, for instance, one or two additional solidification unitsmay be added per each further impingement area.

In the method according to the first aspect of the invention, the gasstream preferably impinges within an above-mentioned central region ofthe build area substantially at a right angle to the build area,particularly at an angle of at least 45°, preferably at an angle of atleast 60°, particularly preferably at an angle of at least 70°. Here,“substantially” firstly means that the non-guided gas stream may billowor, respectively, at least temporarily have no permanent shape duringthe operation of the generative manufacturing apparatus. Secondly, it isa central, inner partial stream of the gas stream according to theinvention that impinges onto the build area typically at an angle from85° to 90°. I.e. the above-mentioned flatter angles generally apply tothe margin areas of the gas stream, which have been, for instance,guided and/or shaped by an inlet nozzle. The substantially rectangularimpingement of the gas stream within a central region of the build areahas an advantage that the gas stream can be subsequently deflected indifferent directions towards the build area edge under substantially thesame conditions. Thereby, a removal of impurities as uniform as possiblealong the entire build area can be achieved.

With a profile of the gas stream showing an expansion in margin regionsin that exterior partial streams of the gas stream have increasinglyflatter angles of impingement onto the build area, on the whole,considerably smoother velocities may be achieved at which the individualportions of the gas stream impinge within the build area andsubsequently flow further across the build area. Compared to a gasstream jet impinging at a right angle, a gas stream jet impinging at anacute angle and having the same velocity typically generates a lowerimpact pressure at the point of the impingement. That way, for a removalof impurities from the process chamber atmosphere to be as effective aspossible, a high volume flow rate or, respectively, a high velocity ofthe gas stream may be set, which nevertheless do not go along withlocally excessive velocities in the vicinity of the build area, whichcould lead to an undesired whirling up of powder from a powder bed ofthe upper building material layer and thus to a reduce of the quality ofa build process and a built part.

In the method according to the first aspect of the invention, afterimpinging within the build area, the gas stream preferably flowssubstantially parallel to the build area towards an edge of the buildarea. In the course of this, a deflection of the gas stream impingingwithin the build area to a substantially parallel flow direction towardsthe edge of the build area takes place in a lower quarter, preferably alower sixth, particularly preferably a lower eighth of a second processchamber height corresponding to a distance between the build area andthe gas supply device in a direction perpendicular to the build area. Inparticular, the top build material layer may function as a baffle forthe gas stream, which, for instance, deflects the gas stream whichapproximately perpendicularly impinges thereon by approximately 90°.

Here, “substantially parallel” may mean that not necessarily the totalvolume of the gas stream is deflected in the same way. Minor deviationsfrom a subsequent parallel flow direction relatively to the build areamay be, in particular, present in the middle of the impinging gasstream. It is preferred that at least 50%, preferably 65%, particularlypreferably 80% of the gas stream be deflected into a directed streamsubstantially parallel to the build area.

The distance corresponding to the second process chamber height is thevertical distance between the build area and that region of theprocess-chamber-sided inlet region of the gas supply device which isnearest to the build area. If this inlet region, for instance, comprisesan inlet protruding from the process chamber ceiling towards the buildarea, such as a nozzle, a tube, or a proboscis, then the above-mentioneddistance is measured from that region of the nozzle, tube, or probosciswhich is nearest to the build area. The closer to the build area thedeflection of the gas stream to the substantially parallel flowdirection takes place, the more intensive is the removal of impuritiesdirectly above the build area, where most of the impurities mentioned atthe beginning are generated.

In the method according to the first aspect of the invention, the outletis preferably arranged in a lower quarter, preferentially a lower fifth,particularly preferably a lower sixth of the above-mentioned secondprocess chamber height. The closer to the build area in the verticaldirection the outlet is arranged, the shorter distances gas streamportions streaming across the build area need to travel until they exitthe process chamber. Thereby, impurities are removed from the processchamber by the shortest route, which reduces the risk of a processdisturbance by impurities.

Furthermore, the outlet may comprise a suction device in order to suckoff the process gas from the process chamber. Such a sucking device maybe arranged at an arbitrary position in the process gas piping system.It may, for instance, comprise a turbine or a kind of propeller, whichprovide for a circulation of the process gas in a gas circuit in whichthe process gas first streams in a controlled manner through the processchamber and is thereafter transported from the outlet back to the gassupply device according to the invention, wherein suitable filters maycleanse the process gas of impurities while it passes through the pipesystem.

In the method according to the first aspect of the invention, theselective solidification is preferably performed by means of asolidification device comprising at least two solidification units. Inthe course of this, a working area within the build area is assigned toeach solidification unit, the working areas being preferablysymmetrically arranged with respect to a central plane or central axisgoing through a central point of the build area perpendicularly to thebuild area (cf. FIGS. 2, 10 a/10 b, and 11 b). This configuration may,in particular, be advantageously combined with the above-describedembodiment having several elongate oval impingement areas of partialstreams of the gas stream within the build area.

However, in many cases, a single elongate oval impingement areaaccording to the invention is already sufficient here for an improvedremoval of impurities from the process chamber. For example, in case ofup to four solidification units whose assigned working areas lie arounda point of the build area, a single impingement area according to theinvention having the same point as its central point may be generated.In other words, in this example, the central point of the impingementarea is arranged centrally between the individual working areas or, asthe case may be, centrally in the region of overlap of the individualworking areas (cf. FIGS. 10b and 11b , in a corresponding sense). Since,after impinging within the build area, the gas stream according to theinvention is deflected in all directions away from the impingement area,the process gas flowing off above the build area towards the build areaedge respectively streams through only one working area in thisconfiguration. Consequently, the gas stream carries impurities from aworking area directly towards the build area edge and not to anotherworking area, so that a multiplication of the number of thesolidification units does not lead to an increase of an amount ofimpurities above a working area. This principle of a central arrangementof impingement areas with respect to working areas can also becorrespondingly transferred to cases where several impingement areas areprovided.

Providing several solidification units makes it possible, for instance,to enlarge a possible build volume and/or to increase possible buildrates by a multiple. In the course of this, a solidification unit may,in particular, be a laser-scanner-unit, or a scanner, or a lineirradiation device.

Working areas may be identical regions within the build area, overlapeach other, or lie side by side without overlapping. Altogether, theworking areas preferably cover substantially the total area of the buildarea, so that the whole build area may be used for the fabrication. Inparticular, the working areas may be arranged axially symmetrically toeach other within the build area. For example, they can possess afour-fold rotational symmetry with respect to an axis of symmetry whichgoes through the central point of the build area and is perpendicular tothe build area.

In the method according to the first aspect of the invention, the gassupply device preferably comprises at least one fastening device fordetachably fastening at least one nozzle for shaping the gas stream. Inthe course of this, the at least one nozzle is selected in advance froma greater quantity of nozzles which can be fastened by means of thefastening device and the at least one nozzle is fastened by means of thefastening device, wherein, by selecting the at least one nozzle, a flowdirection and/or a flow profile of the gas stream in the process chamberis changed. This change of the flow direction may apply to the gasstream according to the invention as a whole, which effects a lateralshifting of its impingement area within the build area. Alternatively oradditionally, the change may apply to a partial stream of the gas streamaccording to the invention, which leads to a change of the geometricshape and/or the size of the impingement area according to theinvention.

Alternatively or additionally, the gas supply device preferablycomprises at least one switchable nozzle for shaping the gas stream,which nozzle is switchable between a functionless state and a functionof injecting the process gas and/or switchable between at least twopredefined designs or, respectively, states of a three-dimensional inletgeometry of the nozzle and/or of an opening cross-section and/or of anorientation of a nozzle opening relatively to the build area and/or to aprocess chamber wall, wherein a suitable combination of at least two ofthe following parameters is selected and adjusted: (i) inflow velocityof the gas stream into the process chamber, (ii) three-dimensional inletgeometry of the nozzle, (iii) opening cross-section of a nozzle opening,as well as (iv) orientation of a nozzle opening relatively to the buildarea and/or to a process chamber wall.

The just described methods according to the present invention forconfiguring the gas supply device are executed individually or incombination with each other, preferably as a function of at least one ofthe following criteria, particularly preferably automatically: (i) ageometry and/or size and/or arrangement of at least one region to besolidified in a top building material layer within the build area, (ii)a position of a recoater inside the process chamber, (iii) a position ofa movable gas supply unit and/or a movable gas discharge unit inside theprocess chamber, (iv) a position of a movable control surface forguiding the process gas into at least one predefined direction insidethe process chamber, (v) selected properties of a building material usedin the building process, e.g. a size and/or a weight of powderparticles, as well as (vi) a signal of a monitoring device formonitoring the building process, which may be e.g. an error signal. Anadvantage of these preferred configurations of the method according tothe invention is that the gas stream can be very flexibly adapted tochanging conditions of the gas flow above the build area and potentiallyin the whole process chamber, e.g. within the scope of a control system,whereby disturbances of the building process caused by impurities can befurther reduced and a permanently high quality of a built component canbe provided for.

A second aspect of the invention is a method of generating a ceiling gasstream in the course of the generative manufacturing of athree-dimensional object in a process chamber by a layer-by-layerapplication and selective solidification of a building material within abuild area arranged in the process chamber. In the course of this, theprocess chamber has a chamber wall having a process chamber ceilinglying above the build area. According to the invention, at leasttemporarily before and/or during and/or after the manufacturing of theobject, a ceiling gas stream of a process gas is passed through theprocess chamber which is streaming from the process chamber ceilingtowards the build area in a controlled manner. The ceiling gas streamaccording to the invention is supplied to the process chamber throughmultiple ceiling inlets formed in the process chamber ceiling which aredistributed over a region of the process chamber ceiling and which aredesigned and/or arranged and/or controlled such that the ceiling gasstream exiting the ceiling inlets is directed substantiallyperpendicularly to the build area downwards onto the build area.

In the course of this, the above-mentioned control or steering of thestreaming behaviour of the ceiling gas stream according to the inventionis carried out by the properties of the ceiling inlets according to theinvention which are firstly generally described above and are describedin more detail below.

The process chamber ceiling region over which the ceiling inlets aredistributed may be a partial region of the process chamber ceiling withregard to its extension or area, or it may alternatively extend over theoverall process chamber ceiling. “Substantially perpendicularly”comprises, in particular, angle ranges of at least 45°, preferably atleast 70°, particularly preferably at least 80° with respect to thebuild area.

By the multiple ceiling inlets of the invention distributed in theprocess chamber ceiling, multiple partial ceiling streams flowingsubstantially vertically downwards towards the build area are generated,immediately pushing impurities present in the process chamber atmospheredownwards towards the build area. In this manner, an almost planevertical process gas stream, a kind of “descending process gas carpet”,having an arbitrarily high level of homogeneity may be generated on thewhole.

By the ceiling gas stream according to the invention it may, thus, beeffectively prohibited that impurities generated while the buildingmaterial is solidified spread upwards towards the process chamberceiling. This way, an accumulation of impurities in upper regions of theprocess chamber and, in particular, a deposition of impurities at acoupling window or another optical device for a radiation needed for theselective solidification may be prevented.

In particular, the method according to the second aspect of theinvention may be advantageously combined with the above-described methodaccording to the first aspect of the invention. In other words, theceiling gas stream according to the invention may be combined with theabove-described gas stream having an elongate oval impingement areawithin the build area (subsequently occasionally subsumed under the term“central gas stream”) in the method according to the invention. Sinceboth of these gas streams of the process gas are substantially alignedin the process chamber—namely substantially vertically downwards towardsthe build area,—they do not disturb one another in their course of flowand, thus, also not in their purging effect. In particular, due tosubstantially the same direction of the ceiling gas stream and thecentral gas stream, process gas vortices, which could disturb theremoval of impurities, are scarcely generated.

The combination of the two aspects of the invention rather unfolds anadvantageous synergy effect since the ceiling gas stream according tothe invention and the central gas stream according to the inventionmutually support each other in removing impurities from the processchamber. Whereas the elongate oval impingement area of the central gasstream provides for an effective removal of impurities directly abovethe build area, all remaining volume regions of the process chamber maybe excessively kept clear of impurities by the ceiling gas stream inthat the ceiling gas stream pushes them downwards towards the build areain an area-wide manner and—with a suitable arrangement of one or moreoutlets,—pushes them there.

In particular, the central gas stream according to the invention havingan elongate oval impingement area may also be considered as a part ofthe ceiling gas stream according to the invention. This may, forinstance, be the case with regard to homogeneous and/or area-wideproperties of the ceiling gas stream.

In the method according to the second aspect of the invention, theceiling inlets are preferably shaped and/or arranged and/or controlledsuch that the ceiling gas stream is substantially homogeneously shapedin a region of the process chamber. The mentioned region comprisesvertically above the build area at least a lowermost tenth, preferablyat least a lowermost fifth, particularly preferably at least a lowermostthird of a process chamber height measured in a vertical direction fromthe build area up to the process chamber ceiling. Alternatively oradditionally, the mentioned region comprises in a plane of the buildarea and/or parallel above the build area at least the area of the buildarea, preferably additionally a surrounding area of the build area,particularly preferably substantially a total area of a process chamberbottom.

A surrounding area of the build area is understood to be a lateral arealextension around the build area, e.g. within a distance of 5 cm aroundthe build area.

The process chamber bottom is understood in the context of the inventionas a structure comprising the build area, i.e. concretely a buildingsupport mentioned at the beginning or an upper building material layerapplied thereto. The process chamber bottom lies under the processchamber ceiling. It is understood as an area in a plane, substantiallywithout a difference in level between the build area and a base platebordering the build area.

In the course of this, the term “homogeneous” presumes a planecharacteristic of the ceiling gas stream without regions in which aprocess gas volume substantially rests or moves in a different orundefined manner. Further, a substantially equal velocity of asubstantially plane ceiling gas stream is presumed. Thus, a continuousdownward movement in a defined spatial region of the process chamberresults for the process gas streaming in.

The homogeneity can be, for instance, measured as a substantiallyuniform impact pressure on a predetermined level of height in theprocess chamber above the build area.

The homogeneity of the ceiling gas stream may, for instance, beinfluenced by a size and/or a density of the distribution of the ceilinginlets in the process chamber ceiling and/or by a uniform or non-uniformcharging of the ceiling inlets with the process gas. Further criteriaare, for example, the number of the ceiling inlets, a total openingcross-section area, and cross-sectional shape(s) of the ceiling inlets.

In the method according to the second aspect of the invention, theprocess chamber preferably has a process chamber bottom lying below theprocess chamber ceiling, and the build area extends over a partial areaof the process chamber bottom.

Further, a distribution of opening cross-section areas of the ceilinginlets at the process chamber ceiling relatively to a total area of theprocess chamber bottom is substantially uniform, wherein the ceilinginlets are designed and/or arranged and/or controlled such that partialceiling streams of the ceiling gas stream exiting the ceiling inlets arerespectively directed substantially perpendicular to the build areadownwards onto the process chamber bottom.

The uniform distribution may, for instance, be achieved by ceilinginlets having the same design and/or opening cross-section area and atleast similar distances from one another.

In particular, for a flatly shaped process chamber ceiling with theprocess chamber ceiling or the process chamber bottom being subdividedinto identical quadrants, a similar number of ceiling inlets perquadrant may be provided. There may also be provided a regulardistribution of ceiling inlets or, respectively, of openingcross-section areas of the ceiling inlets per unit area of the processchamber ceiling. For example, a ratio of an opening area of the ceilinginlets to a process chamber bottom area may always lie between 1/10 and1/30, on average be 1/20, with the process chamber bottom beingsubdivided into 25 or 100 quadrants. In the course of this, the openingcross-section area may be calculated by orthogonally projecting theopenings of the ceiling inlets onto the process chamber bottom such thatfor the ceiling inlets being not completely oriented to the processchamber bottom only a fraction of the actual opening cross-section areais evaluated.

In the course of this, “substantially perpendicular” means that thecross-sections of individual partial streams of the ceiling gas streammay also be expanded, so that e.g. cone-shaped partial streams result.

In the method according to the second aspect of the invention, theceiling gas stream consisting of partial ceiling gas streams may flow ina substantially laminar manner from the process chamber ceiling in thedirection towards the process chamber bottom. In a configurationalternative hereto, a small number of ceiling inlets having a low exitvelocity may be provided, so that each individual jet diameter grows andthe jets become slightly cone-shaped on the way to the build area.

In the method according to the second aspect of the invention, theceiling gas stream is preferably passed through the process chamber atleast temporarily before and/or during and/or after the selectivesolidification of the building material, particularly preferablysubstantially during the whole process of the selective solidification.In the course of this, the ceiling gas stream is preferably also activebetween two solidification processes, e.g. during an operational breakof the solidification process, in order to purge the process chamberatmosphere so that impurities such as smoke cannot billow through theprocess chamber in an uncontrolled manner but are rather reliably keptin a lower region of the process chamber and/or particularly preferablyremoved through an outlet device.

In an advantageous embodiment of the method according to the secondaspect of the invention, the process chamber ceiling comprises a hollowspace having a wall which is substantially closed in an outer wallregion turned away from the process chamber and which possesses ceilinginlets in an inner wall region bordering the process chamber. In thecourse of this, the hollow space serves as an intermediate zone betweenone or several supply pipes to the hollow space and the ceiling inlets,which guide a process gas volume from the hollow space into the processchamber.

The hollow space is preferably shaped in such a manner, particularlywith regard to a suitable height in the direction perpendicular to thebuild area, that a process gas volume streaming in through the supplyline(s) firstly spreads out in the hollow space instead of directlyflowing further towards the process chamber through nearby ceilinginlets. To this end, the inner wall surface may have deflector surfacestowards the hollow space opposite to openings of the supply line(s),which preferably deflect an incoming process gas jet in all directionsinto the hollow space. In an advantageous manner, by filling or,respectively, flooding the hollow space with process gas as extensivelyas possible prior to a further transport into the process chamber, ahomogeneity of the ceiling gas stream may be considerably improved inthat partial streams of the gas stream are streaming into the processchamber from the ceiling inlets at a substantially equal velocity. Inaddition, the hollow space may also lead to a calming of the process gasguided into it in that its velocity is considerably reduced afterescaping from the supply pipe(s) before it streams into the processchamber.

The inner wall region may basically cover an arbitrary portion of thearea of the process chamber ceiling. Preferably, it is a portion aslarge as possible, having the advantage of a better flatness and, thus,homogeneity of the ceiling gas stream. The outer wall region being“substantially closed” in particular means that constructional devicessuch as e.g. supply pipes are an exception.

According to a further development of the above embodiment, the innerwall region is substantially formed by a plate, preferably a perforatedplate. In the course of this, the ceiling inlets are at least partlyformed by holes of the plate or of the perforated plate. In the courseof this, the plate or the perforated plate has at least 10 holes,preferably at least 100 holes, particularly preferably at least 1000holes. Alternatively or additionally in the course of this, an averageopening cross-section area of the holes is not exceeding 10 cm²,preferably not exceeding 2 cm², particularly preferably not exceeding0.1 cm². Also alternatively or additionally in the course of this, a sumof the opening cross-section areas of the holes is not exceeding 20% ofa total area of a process chamber bottom, preferably not exceeding 10%of a total area of the process chamber bottom, particularly preferablynot exceeding 5% of a total area of the process chamber bottom.

The perforated plate may, for instance, be a stamped or perforated plateor a porous sheet made of an arbitrary material. The perforated platemay also, for instance, represent one or more fine-meshed wire grid,e.g. a filter mat. Alternatively, a cartridge having channels of asuitable length may be used for this, their orientation beingsubstantially identically to the flow direction of the ceiling gasstream substantially perpendicular to the build area. Such channels havethe advantage of improving a distribution and shape of the ceiling gasstream by guiding the individual partial ceiling gas streams andadditionally reducing turbulences.

In the method according to the second aspect of the invention, at leastone ceiling inlet and/or at least one additional gas inlet into theprocess chamber is preferably designed and/or controlled such that,depending on a spatial configuration of the process chamber and/or on aposition and/or size of a device arranged inside the process chamber, avelocity and/or an orientation and/or a jet cross-section of a partialceiling gas stream streaming out of the ceiling inlet or the additionalgas inlet are varied prior to and/or during and/or after the objectmanufacturing. In the course of this, the additional gas inlet may, forinstance, be an inlet of the central gas stream according to the abovefirst aspect of the invention.

This configuration makes it possible to purposefully control inlets suchas e.g. nozzles in order to deliberately create in-homogeneous zonesinside the process chamber. Such purposefully generated inhomogeneityzones of the ceiling gas stream may e.g. be advantageous in case ofspecific geometries of the process chamber, for instance, in cases of acraggy or curved configuration of the process chamber wall, or in casesof a variable stream guiding inside the process chamber, such as e.g. byadjustable control surfaces. A selectively higher velocity of specificpartial ceiling gas streams or a purposeful and controlled generation ofvertices may configure the cleaning and keeping free edges, niches etc.in the process chamber, which would otherwise be insufficiently purgedby the process gas, of impurities as more effective.

This is, in particular, also compatible with a homogeneous descending ofthe process gas above the build area and in a surrounding area of thebuild area, e.g. within a lateral distance of 5 cm around the buildarea. When, for example, one or more side walls of the process chamberare curved, a path for partial ceiling gas streams to travel may belonger along the corresponding side wall than in the centre of the buildarea. Now, for an advantageous “homogeneous” shaping of the descendingprocess gas carpet, a velocity of the partial ceiling gas streams may beadjusted to be higher towards the margin regions in such a manner thatthe longer route is compensated and the partial ceiling gas streamsarriving at the process chamber bottom have a similar or equal velocity.

In an advantageous embodiment of the method according to the secondaspect of the invention, the process chamber ceiling has at least onecoupling window for coupling a radiation used for the solidification ofthe building material into the process chamber. Furthermore, in thecourse of this, the ceiling inlets are substantially uniformlydistributed over a total region of the process chamber ceiling exceptfor a region occupied by the at least one coupling window. Beside one ormore coupling windows, such an omitted region in the process chamberceiling may also have, for instance, a camera or further sensor systemsfor process monitoring.

In a further development of this embodiment, the process chamber ceilingand/or the inner wall region has/have at least one central inlet in asection bordering on the at least one coupling window which centralinlet is designed and/or controlled such that, during operation, acentral partial ceiling gas stream streams out therefrom towards thebuild area and is preferably widened in such a manner that the centralpartial ceiling gas stream converges at its margins towards adjacentpartial ceiling gas streams or overlaps with these at least in a lowesttenth, preferably at least in a lowest fifth, particularly preferably atleast in a lowest third of the process chamber relating to a processchamber height between the build area and the at least one couplingwindow lying vertically above it. Thereby, a substantially full-surfacegas stream streaming in a controlled manner towards the build area isgenerated at least across the whole build area and preferablyadditionally in a surrounding area of the build area.

Here, the ceiling gas stream does not need to be homogeneous with regardto its velocity in the sense of the above definition. For instance,here, the central partial ceiling gas stream may have a higher velocitythan the remaining partial ceiling gas streams in order to achieve aparticularly effective removal of impurities.

Here, the widening is understood as relating to the cross-section of thepartial ceiling gas stream. It may, for instance, take place in acone-shaped manner in order to also direct the central partial ceilinggas stream into regions of the process chamber in which a process gasvolume would otherwise substantially rest or move in an undefined mannersince they are not directly charged by a ceiling gas stream which ise.g. streaming out of the hollow space. This may, in particular, be thecase for regions lying below a coupling window.

In other words, a widening preferably takes place here to such an extentthat contours of projections, to be specific not orthogonal projections,of three-dimensional inner walls of the central inlet and of thedirectly neighbouring ceiling inlets onto the build area converge,touch, or overlap one another, whereby a substantially homogeneousceiling gas stream is shaped at least in a lowest tenth, preferably atleast in a lowest fifth, particularly preferably at least in a lowestthird of a process chamber height.

In this further development, particularly preferably, a plurality ofsuch central inlets are arranged around the coupling window or thecoupling windows in order to achieve a homogenisation of the ceiling gasstream. In the course of this, the inlet nozzles may also be designedsuch that partial ceiling gas streams being asymmetrical in thecross-section are generated.

In an advantageous embodiment of the method according to the secondaspect of the invention, at least temporarily prior to and/or duringand/or after the manufacturing of the object, the process gas issupplied to the process chamber in a preferably closed process gascircuit and is discharged from the process chamber through an outlet. Inthe course of this, the ceiling gas stream represents at least a part ofthe process gas circuit. Further, in the course of this, supply and/ordischarge pipes of the process gas circuit comprise a conveying unit bymeans of which a velocity and/or velocity distribution and/or pressuredistribution of a total process gas stream or of the ceiling gas streamin the process chamber is varied prior to and/or during and/or after themanufacturing of the object.

In the course of this, the supply/discharge may take place steadily,continuously, dynamically, in regular and/or irregular intervals etc.The conveying unit may, for instance, comprise a switchable pump,turbine, or pump turbine, and/or also a propeller. By theabove-mentioned variation of the ceiling gas stream, in particular alsoin relation to the total process gas stream, the process gasdistribution in the process chamber and/or the removal of impuritiestherefrom can be controlled and be adapted that way, for instance, tospecific properties of the process chamber and the object to bemanufactured in a concrete application case and/or to specific processphases. That way, the process gas throughput of the total process gasstream or of the ceiling gas stream in the process chamber may be, inparticular, increased in process phases having an increased impuritygeneration.

In an advantageous further development of this embodiment, the processgas circuit comprises in addition to the ceiling gas stream at least oneof the following gas streams for removing of impurities generated duringthe solidification of the building material from the process chamber:

a central gas stream supplied to the process chamber at leasttemporarily prior to and/or during and/or after the manufacturing of theobject by means of a central inlet formed in the process chamber ceilingand discharged from the process chamber via at least one outlet, thecentral gas stream impinging within a central region of the build areasubstantially at a right angle to the build area, particularly at anangle of at least 45°, preferably at an angle of at least 60°,particularly preferably at an angle of at least 70° (cf. FIG. 13),

a lateral gas stream supplied to the process chamber at leasttemporarily prior to and/or during and/or after the manufacturing of theobject via a side inlet arranged at a build area side and dischargedfrom the process chamber via at least one outlet arranged at an oppositeside of the build area, preferably such that the lateral gas streamflows in a substantially laminar manner substantially across apreferably total area of the build area (cf. FIG. 14).

In the course of this, an impingement area of the central gas streamwithin the build area may have an arbitrary shape. The shape of theimpingement area may, for example, be circular. In the case of a centralgas stream representing the gas stream according to the first aspect ofthe invention described further above, its substantially elongate ovalimpingement area may be regular up to elliptical or, alternatively,irregular. The shape of the impingement area may also be variable duringoperation, e.g. when a recoater moves across the build area in order toapply a building material layer and, in the course of this, deflects thecentral gas stream or, respectively, makes it instable for a certainperiod of time. It may be shaped or, respectively, selected in aninterdependency with a design, arrangement, and/or control of one orseveral outlets.

As described further above with regard to the first aspect of theinvention, the central region within the build area may also hereoccupy, for instance, no more than approximately 60%, preferably no morethan approximately 20%, particularly preferably no more thanapproximately 10% of a total area of the build area.

In a further advantageous development of the above embodiment, apreferably adjustable volume ratio of the ceiling gas stream to thecentral gas stream and/or to the lateral gas stream in the process gascircuit is at least 1:1, preferably at least 2:1, particularlypreferably at least 3:1, and/or not exceeding 7:1, preferably notexceeding 6:1, particularly preferably not exceeding 5:1. By such avolume ratio, for instance, a concrete build area size and/or processchamber height from the build area up to the process chamber ceiling inan application case can be taken into account.

In a further advantageous development of the above embodiment, a ratioof a total inlet opening area to a total outlet opening area of theprocess gas circuit is varied prior to and/or during and/or after themanufacturing of the object. Thereby, a velocity and/or a pressure ofthe process gas is/are varied at least in a partial region of theprocess chamber. That way, alternatively or additionally to anabove-mentioned adjustable conveying unit, the velocity of the processgas recirculation in the process gas circuit may be advantageouslyvaried or adapted.

In the method according to the second aspect of the invention, theselective solidification is preferably performed by means of asolidification device comprising at least two solidification units. Inthe course of this, a working area within the build area is assigned toeach solidification unit. The working areas are preferably symmetricallyarranged with respect to a central plane or central axis going through acentral point of the build area perpendicularly to the build area. Inparticular, the description set forth further above with regard toseveral solidification units with regard to the first aspect of theinvention applies here correspondingly.

A further aspect of the invention is a control unit for an apparatus forgeneratively manufacturing a three-dimensional object, the control unitbeing designed/arranged for generating control commands for thepreferably automatic execution of a method according to the first and/orsecond aspect of the invention.

A still further aspect of the invention is an apparatus for generativelymanufacturing a three-dimensional object, the apparatus being designedand/or controlled to preferably automatically execute a method accordingto the first and/or second aspect of the invention. Therein, the controlmay, for instance, be carried out by means of the control unit accordingto the invention. The manufacturing apparatus according to the inventioncomprises a process chamber for manufacturing the object by alayer-by-layer application and selective solidification of a buildingmaterial within a build area arranged in the process chamber.

Further, with the first aspect of the invention, the apparatus comprisesa gas supply device for supplying a process gas to the process chamberduring the manufacturing of the object as well as an outlet fordischarging the process gas from the process chamber. In the course ofthis, according to the invention, the gas supply device is designedand/or arranged relatively to the build area and/or controlled such thata gas stream of the process gas streaming through the process chamber isshaped in such a manner that at least one substantially elongate ovalimpingement area of the gas stream is generated within the build area.

With the second aspect, the process chamber of the apparatus accordingto the invention has a chamber wall having a process chamber ceilinglying above the build area. According to the invention, multiple ceilinginlets are formed in the process chamber ceiling for supplying a ceilinggas stream to the process chamber which are distributed over a region ofthe process chamber ceiling and which are designed and/or arrangedand/or controlled such that the ceiling gas stream exiting the ceilinginlets is directed substantially vertically downwards onto the buildarea.

As for the rest, the description set forth further above with regard tothe method according to the invention correspondingly applies to themanufacturing apparatus according to the first and/or second aspect ofthe invention.

In the following, the above-mentioned and further features and effectsof the invention are described in more detail with the help of exemplaryembodiments with reference to the drawings. The demonstration of themanufacturing apparatus, the central gas stream according to theinvention, which will also be in short simply denoted by “gas stream” inthe first aspect, its impingement area within a build area, and theceiling gas stream according to the invention (second aspect of theinvention) is merely schematic in the drawings and is therefore not tobe understood as true to scale. Same or corresponding elements aredenoted in different examples by same or corresponding reference signs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional side view of an embodiment of themanufacturing apparatus according to the invention having at least onesolidification unit;

FIG. 2 is a schematic cross-sectional side view of a further embodimentof the manufacturing apparatus according to the invention having atleast two solidification units;

FIG. 3 is a schematic view of a gas stream having a conventionalcircular impingement area within the build area flowing off towards thebuild area edge (in top view);

FIG. 4 is a schematic view of a gas stream having a conventionalelongate rectangular impingement area within the build area flowing offtowards the build area edge (in top view);

FIG. 5 is a schematic view of a gas stream flowing off towards the buildarea edge in the vicinity of a “long side” of an elongate ovalimpingement area according to the invention within the build area (intop view);

FIG. 6 is a schematic view of a gas stream flowing off towards the buildarea edge in the vicinity of a “narrow side” of an elongate ovalimpingement area according to the invention within the build area (intop view);

FIG. 7 is a schematic top view of an example of the arrangement of abuild area in the process chamber of a manufacturing apparatus accordingto the invention with flow lines of the gas stream above the build area;

FIG. 8 is a schematic cross-sectional side view of an arrangement of aninlet relatively to a build area with flow lines of the gas streamaccording to the invention in the process chamber;

FIGS. 9a and 9b are schematic top views of examples of an inlet of a gassupply device according to the invention having an expanding effect;

FIG. 9c shows two side views rotated by 90° with respect to each otherof a further example of an inlet of the gas supply device according tothe invention having an expanding effect;

FIG. 9d schematically shows a process-chamber-sided top view on the leftand a perspective view on the right of the inlet of FIG. 9 c;

FIG. 10a is a schematic cross-sectional side view of a process chamberof a manufacturing apparatus according to the invention having foursolidification units (with a laser beam path);

FIG. 10b is a schematic top view of working areas of the foursolidification units within the build area of the process chamber ofFIG. 10 a;

FIG. 11a is a schematic top view of an example of a build area extensionin a manufacturing apparatus according to the invention by threeimpingement areas of the gas stream stringed together;

FIG. 11b is a schematic top view of an example of a build area extensionin a manufacturing apparatus according to the invention whosesolidification device has six solidification units;

FIG. 12a is a schematic cross-sectional side view of the process chamberof a manufacturing apparatus according to the invention having a ceilinggas stream;

FIG. 12b is a schematic top view of the build area and of the ceilinginlets in the manufacturing apparatus of FIG. 12 a;

FIG. 13 is a schematic cross-sectional side view of a manufacturingapparatus according to the invention in which a central gas stream iscombined with a ceiling gas stream in a process gas circuit;

FIG. 14 is a schematic cross-sectional side view of a manufacturingapparatus according to the invention in which a lateral gas stream iscombined with a ceiling gas stream in a process gas circuit;

FIG. 15 is a schematic perspective view of a perforated metal plate forgenerating the ceiling gas stream according to the invention;

FIG. 16 is a schematic perspective view inclined from below onto theperforated metal plate of FIG. 15 in a built-in state in the ceiling ofa process chamber;

FIG. 17 is a schematic perspective view inclined from above and partlyin a vertical cross-section onto a process chamber having a perforatedmetal plate of FIGS. 15 and 16 built-in in its ceiling.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 1, an embodiment of an apparatus 1 for generativelymanufacturing a three-dimensional object is described, the apparatusbeing designed and/or controlled to preferably automatically execute amanufacturing method according to the invention. The layer manufacturingapparatus 1 schematically shown in FIG. 1 is a laser sintering of lasermelting apparatus. For manufacturing a three-dimensional object 2 by alayer-by-layer application and selective solidification of a buildingmaterial, it contains a process chamber 3 having a chamber wall 4comprising a process chamber ceiling 4 a.

In the process chamber 3, an open-top container 5 having a containerwall 6 is arranged. In the container 5, a support 7 movable in avertical direction V is arranged at which a base plate 8 is mountedwhich closes the container 5 below and thereby forms its bottom. Thebase plate 8 may be a plate formed separately from the support 7, whichis attached to the support 7, or it may be integrally formed with thesupport 7. Depending on a building material used (in particular, powder)and a process, a platform 9 may further be mounted on the base plate 8as building support, on which the object 2 is built up. However, theobject 2 may also be built up on the base plate 8 itself, which thenserves as a building support. In FIG. 1, the object 2 to be built in thecontainer 5 on the platform 9 is shown below a build area 10 defined bythe upper edge of the container wall 6 in an intermediate state withseveral layers being already solidified, surrounded by building material11 remaining non-solidified.

The laser sintering apparatus 1 further contains a storage container 12for a building material 13 which can be solidified by an electromagneticradiation and is, in this example, in powder form and a recoater 14movable in a horizontal direction H for applying the building material13 layer-by-layer onto the building support or onto a previously appliedlayer within the build area 10. Optionally, a radiation heater 15 isarranged in the process chamber 3 for heating the applied buildingmaterial 13. As radiation heater 15, e.g. an infrared radiator mayserve.

In order to selectively solidify the applied building material 13, thelaser sintering apparatus 1 contains a solidification device 30 (alsoreferred to as irradiation device in the following) having a laser 31generating a laser beam 32. The laser beam 32 is deflected via adeflecting device 33 and is focused by a focusing device 34 via acoupling window 35, which is mounted in the process chamber ceiling 4 a,onto the building support or a previously applied layer of the buildingmaterial 13. The solidification device 30 may basically also comprisefurther solidification units, which are not seen in the cross-sectionalside view of FIG. 1, having further lasers and/or deflecting andfocusing devices and/or coupling windows.

The laser sintering apparatus 1 further contains a control unit 39 viawhich the individual components of the apparatus are controlled(indicated by arrows in FIG. 1) in a coordinated manner for executingthe building process, in particular, a method according to theinvention. Alternatively or additionally, a control unit may also bepartially or completely be arranged outside the apparatus 1. The controlunit may contain a CPU whose operation is controlled by a computerprogram (software). The computer program may be stored separately fromthe apparatus on a storage medium, from which it can be loaded into theapparatus, in particular, into the control unit 39. The control unit ispreferably a control unit according to the invention.

During operation, the building support, which is a surface of theplatform 9 in this example, is located at the beginning of themanufacturing process at the height of the build area 10 and isrespectively lowered for applying a building material layer by a heightcorresponding to the desired layer thickness.

By moving the recoater 14 within the build area 10, a layer of thebuilding material 13 in powder form (pulverulent) is respectivelyapplied to the building support or a pre-existing upper powder layer.The application takes place at least over the total respectivecross-section of the object 2 to be manufactured. Optionally, thepulverulent building material 13 is heated up by means of the radiationheater 15 to an operating temperature. Subsequently, the cross-sectionof the object 2 to be manufactured is scanned by the laser beam 32, sothat the pulverulent building material 13 is solidified at the pointscorresponding to the cross-section of the object 2. These steps arerepeated as long as until the object 2 is completed.

According to the invention, a gas stream 40 of a process gas is suppliedto the process chamber 3 through a gas supply device (not shown)arranged in the process chamber ceiling 4 a while the object 2 is beingmanufactured in order to remove impurities generated in the course ofthe selective solidification from the process chamber 3. Aprocess-chamber-sided inlet of the gas supply device (not shown inFIG. 1) may have an arbitrary suitable arrangement in the processchamber ceiling 4 a and form. The gas stream 40 exits the processchamber 3 through outlets 42 a and 42 b arranged at opposed build areasides approximately at the height of the build area. The outlets 42 aand 42 b are merely schematically indicated in FIG. 1. They may have anysuitable arrangement and geometry, in particular according to thefurther-above-described advantageous configurations of the invention. Inparticular, the outlets 42 a and 42 b may be arranged in or at thechamber wall 4, directly at the build area edge or at a distancetherefrom, as well as not necessarily at the height of the build area.

After exiting the gas supply device, the gas stream 40 streams throughthe process chamber 3 in a non-guided manner and substantiallyvertically, this means except for a possible billowing of the gas stream40 and a minor deviation of margin regions of the gas stream 40 by up toapproximately 20° from a vertical with respect to the build area 10,towards the build area 10. There, the gas stream 40 impinges in animpingement area A3 according to the invention, which lies centrallywithin the build area 10, onto the upper building material layer and islaterally deflected partly by the upper building material layer, partly,as the case may be, by a suction effect of the outlets 42 a and 42 b.Subsequently, the gas stream flows off, preferably substantiallyparallel to the build area 10, towards the outlets 42 a and 42 b andthereby removes impurities from the process chamber 3.

FIG. 2 shows a further embodiment of the manufacturing apparatus 1according to the invention. In differs from the apparatus of FIG. 1 inthe configuration of the solidification device 30 and in a specificconfiguration of a process-chamber-sided inlet of the gas supply device.

The manufacturing apparatus 1 in FIG. 2 is a so-calledmulti-scanner-machine since the solidification device 30 comprisesseveral solidification units. In the cross-sectional side view of FIG.2, two of them can be seen. Components of the one solidification unit 30a on the left in the figure are denoted by an additional index “a”,those of the other one solidification unit 30 b on the right in thefigure by an additional index “b”.

By way of example only, each solidification unit comprises a laser 31a/31 b generating a laser beam 32 a/32 b, as well as a deflecting device33 a/33 b, a focusing device 34 a/34 b, and a coupling window 35 a/35 b.Alternatively, a solidification unit may also comprise only one or apart of the above-mentioned elements.

To each solidification unit, a working area (in FIG. 2 on the left andon the right) within the build area 10 is assigned which can be scannedby the respective laser beam 32 a or 32 b. In this example, the workingareas are arranged axially symmetrically with respect to a central planewhich goes through a central point Z0 of the build area and isperpendicular to the build area 10 and to the drawing plane.

The apparatus 1 may have further pairs of solidification units which arenot to see in the cross-sectional side view of the FIG. 2 and which arepreferably arranged and/or designed similarly to FIG. 2. An example of afour-scanner-machine having four solidification units on the whole isdescribed further below referring to FIGS. 10a and 10b . Furthermore,referring to FIGS. 11a and 11b , an example of a six-scanner-machinehaving six solidification units on the whole is described.

Further, the gas supply device (not shown) ends in FIG. 2 in aprocess-chamber-sided inlet 43, which may, for instance, be a nozzle.The nozzle 43 protrudes from the process chamber ceiling 4 a notsubstantially, here, by way of example only, by approximately 4 cmdownwards into the process chamber 3 with a process chamber heightmeasured vertically from the build area 10 up to a coupling window 35a/35 b being approximately 49 cm. Alternatively, the inlet 43 may alsoprotrude deeper or, alternatively, not protrude at all into the processchamber 3.

In FIG. 2, the nozzle 43 is arranged approximately centrally between thecoupling windows 35 a and 35 b of the two solidification units 30 a and30 b shown. Since the gas stream 40 streams substantially verticallydownwards towards the build area 10, the impingement area A3 of the gasstream 40 also lies centrally in the build area and, thus, in bothworking areas which can be scanned by the two laser beams 32 a or 32 bwithin the build area 10. That way, each working area is flownover/through by its own gas stream portion flowing in FIG. 2 either tothe left or to the right from the centre Z0 of the build area.Therefore, impurities generated in the respective working areas areremoved by the respective gas stream portions on the shortest routetowards the build area edge. Consequently, the two lasers 31 a and 31 bdo not mutually disturb one another with regard to the impurities whichthey cause in the manufacturing process by irradiating the powder.

Subsequently, the advantageous effects of an elongate oval impingementarea according to the first aspect of the invention as compared to theconventional circular or elongate rectangular impingement areas, whichadvantageous effects have been set forth above with reference to FIGS. 3to 6, will be further described and supplemented referring to FIGS. 7 to11.

FIG. 7 shows in a schematic top view an example of the arrangement ofthe build area in the process chamber of a manufacturing apparatusaccording to the invention with flow lines of the gas stream above thebuild area. In particular, it may be the apparatus 1 of FIG. 1 or 2.

In this example, the build area 10 has a rectangular build area edge BR,which may preferably be quadratic and may, for instance, be 400 mm×400mm. Here, also the chamber wall 4 of the process chamber 3 isrectangular in a horizontal cross-section at a height of the build area.By way of example only, symmetry axes of both rectangles coincide.Around the build area 10, a process chamber bottom 4 b is shown, lying,for example, approximately at the height of the build area.

Symmetrically arranged with respect to a centre Z0 of the build area 10,there is the elongate oval impingement area A3 of the gas streamaccording to the invention. In this example it is elliptical, having along axis of the ellipse parallel to a narrow side of the build area. Adashed line shows an orthogonal projection of the process-chamber-sidedopening of an inlet of the gas supply device (for example, the nozzle 43in FIG. 1 or 2). In particular by an expanding effect of the inlet, i.e.an effect of widening a cross-section of the gas stream towards thebuild area, the impingement area A3 is larger than the projection of theopening of the inlet onto the build area 10.

After impinging within the impingement area and the deflection, the gasstream flows along the build area 10 and the process chamber bottom 4 btowards the outlets 42 a and 42 b, which, by way of example only, extendover the whole respective narrow side of the chamber wall 4 parallel tothe narrow sides of the build area. In particular, the outlets 42 a and42 b extend here on their both ends beyond the respective build areaside.

Due to a distance D, which may, for instance, be 10 to 20 cm or larger,between an outlet 42 a/42 b and the nearest narrow side of the buildarea 10, a suction effect exerted, as the case may be, by the outlet onthe gas stream volume is relatively small above the build area 10.Therefore, the deflection of the gas stream after the impingement mainlytakes place due to the rebound of the gas stream at the upper buildingmaterial layer within the impingement area A3 and due to a subsequentflowing off of the gas stream portions into respective nearby regionswhich are not charged by the gas stream afterflow, the latter beingcontinuous at least during the solidification. The flow lines of the gasstream portions flowing off towards the outlets 42 a, 42 b after thedeflection are indicated by continuous curved lines.

Additional outlets may be provided at the long sides of the chamber wall4, in particular centrally, in order to support the discharging of thegas stream portions flowing off at the “narrow sides” of the ellipse A3from the process chamber.

FIG. 8 is a schematic cross-sectional side view of an example of flowlines of a gas stream according to the invention in the process chamber,which may be part of the manufacturing apparatus 1 of FIG. 1 or 2. Thegas stream 40 streams into the process chamber 3 through the inlet 43,which may e.g. be designed as a nozzle. With regard to the constructionof the nozzle 43, for instance, the descriptions referring to FIG. 7 or9 a may apply here.

The nozzle 43 has an inner cross-section length Li (which lies in thedrawing plane of FIG. 8) growing in a vertical direction towards thebuild area 10. Due to this, the gas stream 40 passing through the nozzle43 gets wider in the direction of this inner cross-section length or,respectively, it gets expanded.

In the course of this, however, an inner cross-section area of thenozzle 43 preferably remains substantially constant over the extensionof the nozzle 43 in the direction towards the build area 10, so that thevelocity of the gas stream 40 also remains substantially unchanged as itpasses through the nozzle 43.

Due to the expanding effect of the nozzle 43, in the drawing plane ofFIG. 8, an outer gas flow line of the gas stream 40—it is indicated by acontinuous line—deviates e.g. by approximately 20° from a vertical)(90°with respect to the build area 10. The vertical approximatelycorresponds to the direction of a central gas stream flow line streamingtowards the centre Z0 of the build area 10, which is also indicated by acontinuous line. Depending on a gas stream density and/or suction effectof the outlet, the course of the gas flow lines in margin regions of thegas stream 40 may get flatter (indicated by a dashed line in FIG. 8).

With a constant inner cross-section area of the nozzle 43 over itsextension, the gas stream 40 is simultaneously concentrated in thenozzle 43 in a direction perpendicular to the drawing plane (in FIG. 8not visible). This will be subsequently visualized in further exampleswith the aid of FIGS. 9a -9 d.

Referring to FIGS. 9a-9d , in the following, several examples of aninlet of the gas supply device in form of a nozzle having an expandingeffect on the gas stream according to the invention are described. Inthe course of this, the gas supply line (not shown) ending in the nozzlehas, by way of example only, always a circular inner cross-section.Further, also here the nozzle preferably has, similarly to FIG. 8, asubstantially constant inner cross-section area for the gas streamflowing through the nozzle. The nozzles shown in FIGS. 9a-9d may, inparticular, be employed in the manufacturing apparatus 1 described withreference to FIGS. 1-8.

FIG. 9a schematically shows in a top view a first embodiment of such anozzle, which may, for example, be the nozzle 43 of FIG. 2 or 8. Acircular pipe-sided inner cross-section 50 of the nozzle is shown by adashed line. In this embodiment, a process-chamber-sided innercross-section 60 (here, at the same time an opening area) of the nozzlehas the shape of an ellipse which is concentric with the gas supplypipe. The opening area 60 does not necessarily need to be elliptical, itrather may be an arbitrary elongate oval having two perpendicularsymmetry axes 61 and 62 as shown.

FIG. 9b shows a schematic top view of a second embodiment of the nozzlewhich differs from the one of FIG. 9a only in that the short axis of theellipse is parallel shifted to the left by a distance dl from avertically drawn symmetry axis of the circular inner cross-section 50.The long axis a of the ellipse still coincides in the top view of FIG.9b with a horizontally drawn symmetry axis of the circular innercross-section 50.

Such an offset dl may be used for a preferably minor deflection of thegas stream as it passes through the nozzle, in order to effect acorresponding shifting of its impingement area within the build area.The offset dl may, for instance, be approximately 3 mm with a long axisa of the ellipse being approximately 75 mm. In the course of this,deviations from a concentric arrangement of the two inner cross-sections50 and 60 are preferably small, in order to avoid undesired turbulencesof the gas stream streaming out of the nozzle at any rate.

FIGS. 9c and 9d show a third embodiment of an inlet of the gas supplydevice in form of a nozzle 43 having a partially expanding effect on thegas stream according to the invention. This nozzle differs from the oneof FIG. 9b in that its process-chamber-sided opening area 60 extends ina direction of its longitudinal axis 61 considerably farther to one sidethan to the opposite side with respect to a central axis 55 of thecircular gas supply pipe. In this manner, the shaping of the gas streamaccording to the invention may be adapted to specific, for instance,asymmetric spatial conditions in the process chamber. In the course ofthis, in particular, the process-chamber-sided opening area 60 of thenozzle may also be designed arbitrarily strongly asymmetric along itslongitudinal axis 61, whereas FIGS. 9c-9d show by way of example only anelliptical opening area 60. As for the rest, the above description withregard to FIGS. 9a and 9b may correspondingly apply here.

FIG. 9c schematically shows two side views of the nozzle 43 rotatedrelatively to one another by 90° around the central axis 55 of thesupply pipe. The left side view is, as in FIG. 8, aligned with respectto an inner cross-section length Li of the nozzle 43 which grows in adirection vertically towards the build area 10 (not shown). As in FIG.8, the gas stream 40 according to the invention (not shown) is expandedin a direction of the growing inner cross-section length Li as it passesthrough the nozzle 43. The right side view shows a taper of the nozzle43 in a direction perpendicular hereto with a constant innercross-section area, whereby the gas stream 40 is concentrated.Altogether, this results in a process-chamber-sided elongate ovalopening area 60 of the nozzle 43, which leads to an elongate ovalimpingement area of the gas stream 40 within the build area 10 accordingto the invention (as, for instance, illustrated in FIG. 7).

Further, FIG. 9d shows on the left a schematic process-chamber-sided topview (i.e. a view from below) of the nozzle of FIG. 9c and on the rightits schematic perspective view. For being detachably fastened at theprocess chamber ceiling 4 a, the nozzle 43 in FIGS. 9c and 9d has at itsend with the circular inner cross-section 50 an external thread 56representing the fastening device according to the invention. In thisexample, the process chamber ceiling 4 a (not shown) has a complementaryinner thread.

In a not shown fourth embodiment of an inlet of the gas supply device inform of a nozzle having an expanding effect on the gas stream accordingto the invention, the process-chamber-sided opening area is notelliptical but rather only axially symmetrical with respect to itslongitudinal extension, being, however, irregularly oval-shaped apartfrom that. Thus, such a nozzle possesses only one axis of symmetry (itslongitudinal axis) and is, beyond that, not concentric with the gassupply pipe ending in the nozzle. As for the rest, the above descriptionwith regard to FIGS. 9a-9d correspondingly applies here.

FIG. 10a shows a schematic cross-sectional side view of a processchamber of a manufacturing apparatus according to the invention havingfour solidification units, only two of which are to see in thecross-sectional side view. In particular, it may be an apparatus 1 ofFIG. 2. In this example, each solidification unit 30 a and 30 bcomprises a laser and a focusing optics, which generate a laser beam 32a/32 b which can scan an assigned working area 10 a/10 b of a build area10.

FIG. 10b shows a (by way of example only) quadratic build area of FIG.10a in a schematic top view. In this example, four working areas 10 a,10 b, 10 c, and 10 d of the four solidification units are identicalquadrants completely covering the build area 10. They respectivelyoverlap each other at sides facing each other. The overlapping regionsare shown as hatched. For the sake of better illustration, a side of theworking area 10 c is shown. An elongate oval impingement area accordingto the invention may be arranged here, for instance, as in FIG. 11b withrespect to working areas 10 a-10 d.

FIG. 11a schematically shows in a top view an example of a build areaextension in a manufacturing apparatus according to the invention bystringing together three elongate oval impingement areas of the gasstream according to the invention.

As for the rest, the above description with regard to FIGS. 1-10 mayapply in this example.

By way of example only, here, three impingement areas A3 are similarlyformed (elliptically, for instance, as in FIG. 7) and similarlyoriented. They also share a common axis of symmetry (not shown), whichis, respectively, the long axis of the ellipse. Furthermore, this commonaxis of symmetry also coincides with the long axis of symmetry of therectangular build area 10. The impingement areas A3 overlap each otherat narrow sides of the ellipses facing each other. Altogether, thisresults in a nearly uniform stream course of the impinging gas streamaccording to the invention along the build area 10, wherein, afterimpinging, the gas stream predominantly flows off on a short, nearlystraight route from the impingement area to the respective outlet 42 aor 42 b. As for the rest, the above description with regard to FIG. 7correspondingly applies here.

FIG. 11b schematically shows in a top view a further example of a buildarea extension in a manufacturing apparatus according to the invention.Here, in contrast to FIG. 11a , only two elongate oval impingement areasof the gas stream are stringed together. As for the rest, the abovedescription with regard to FIG. 11a correspondingly applies also in thisexample.

In FIG. 11b , the build area 10 is subdivided in six partiallyoverlapping working areas 10 a-10 f of six solidification units of thesolidification device. As for the rest, the above description withregard to a four-scanner-machine with reference to FIGS. 10a /10 bcorrespondingly applies here. Also here, by way of example only, theworking areas 10 a-10 f are equal, they are preferably respectivelyquadratic in shape. For a better illustration, the working area 10 a ishighlighted by hatching.

In FIG. 11b , the common axis of symmetry of the two impingement areasA3 passes substantially centrally through the build area 10. This commonaxis of symmetry passes centrally and symmetrically with respect to therow of the working areas 10 a, 10 d, and 10 e arranged on the left inthe figure and the row of the working areas 10 b, 10 c, and 10 farranged on the right in the figure. As already mentioned further above,such a central symmetrical arrangement of the impingement areas withrespect to the working areas 10 a-10 f has, inter alia, the advantage ofshort, nearly straight routs for the gas stream flowing off to theoutlets 42 a/42 b after its impingement. Moreover, that way, theindividual working areas are streamed over by respective different,their own gas stream portions, so that impurities above one of theworking areas do not or scarcely get to the other working areas, so thatthe increased number of solidification units does not negatively affectthe removal of impurities above the build area.

With the build area allocation as in FIG. 11b in a six scanner lasersintering system, in the above-mentioned preferably closed process gascircuit of a central gas stream according to the invention and a ceilinggas stream according to the invention, the volume ratio of the ceilinggas stream to the central gas stream may, for instance, be 5:1. Theresulting six volume parts of the process gas can then be, for instance,discharged from the process chamber through respectively three outletsarranged at both long sides of the build area (in particular,respectively one at a working area).

FIG. 12a is a schematic cross-sectional side view of the process chamberof a manufacturing apparatus according to the invention having a ceilinggas stream. The manufacturing apparatus may, in particular, be the lasersintering apparatus 1 described with reference to FIGS. 1-11. Throughceiling inlets 45 (indicated by continuous arrows) arranged in a processchamber ceiling 4 a, a ceiling gas stream 44 (indicated by dashedarrows) is supplied to the process chamber 3. This one descendsvertically in form of a substantially homogeneous process gas carpetfrom the process chamber ceiling 4 a onto the process chamber bottom 4 blying below it and being formed by the build area 10 and itssurrounding, which corresponds to the remaining region of the processchamber bottom 4 b here. A beam path of a solidification device, whichmay comprise one or more, e.g. four, solidification units havingrespectively one laser, is schematically indicated by two sides of atriangle 32 passing the process chamber 3.

FIG. 12b is a schematic top view on the build area 10 and on the ceilinginlets 45 in the manufacturing apparatus of FIG. 12a . In this example,the ceiling inlets 45 are substantially uniformly distributed over atotal region of the process chamber ceiling 4 a, with the exception of aregion occupied by a coupling optics (for instance, coupling window, notshown) for the solidification radiation, for generating a substantiallyhomogeneous ceiling gas stream 44.

FIG. 13 is a schematic cross-sectional side view of a manufacturingapparatus according to the invention in which a central gas stream iscombined with a ceiling gas stream in a closed process gas circuit. Themanufacturing apparatus may, for instance, possess properties describedwith regard to FIGS. 1-12, the process chamber 3 may, in particular, bedesigned similarly to that of FIG. 12a /12 b.

Supply pipes 46 a and discharge pipes 46 b of the process gas circuitcomprise a conveying unit 47, which, in this example, combines a turbineand additionally a filter in a recirculation-filter-device. The filterserves for removing impurities from the process gas discharged from theprocess chamber 3.

In a regulated or unregulated splitting unit 48, a process gas suppliedto the process chamber 3 via ceiling inlets 45 is split into a ceilinggas stream 44 according to the invention and a central gas stream 40(for instance, according to the first aspect of the invention). Thissplitting is monitored and/or regulated depending on requirements of theconcrete application by using metering points 51 arranged in varioussupply pipe branches. The metering points may, for instance, measure therespective process gas stream. The regulation may, for example, becarried out depending on the constructional design of the processchamber 3 and/or on a concrete fabrication process.

FIG. 14 is a schematic cross-sectional side view of a manufacturingapparatus according to the invention in which a lateral gas stream iscombined with a ceiling gas stream in a closed process gas circuit. Theapparatus in FIG. 14 differs from the one of FIG. 13 only in that alateral gas stream 49 is supplied to the process chamber 3 instead ofthe central gas stream 40.

The lateral gas stream 49 flows substantially parallel and preferably ina laminar manner above the build area 10. It is supplied to the processchamber 3 via a side inlet of the supply pipe 46 a arranged at one buildarea side and discharged from the process chamber via an outlet of thedischarge pipe 46 b arranged at an opposite build area side.

FIG. 15 is a schematic perspective view of a perforated metal plate forgenerating a ceiling gas stream according to the invention in a processchamber, whose ceiling has a hollow space for this (not shown). In otherwords, the perforated metal plate 52 in FIG. 15 is an example for aninner wall region of such a hollow space according to the invention. Inthis example, the perforated metal plate 52 has a plurality of holes 53representing ceiling inlets according to the invention.

The perforated metal plate 52 further has a larger inner opening 54 inits central region which, in a built-in state of the perforated metalplate 52 in the process chamber ceiling 4 a surrounds inter aliacoupling windows 35 a, 35 b for coupling the solidification radiationinto the process chamber 3. In the advantageous configuration as shown,the perforated metal plate 52 has a number of approximately 2000 holes53 on the whole, which are distributed over the perforated metal plate52 substantially —in particular, with the exception of the inner opening54 as well as two approximately hexagonal areas 71 which serve asbaffles for deflecting gas streams, which guide into the hollow space(not shown) of the process chamber ceiling 4 a and thus provide for anequal or approximately equal velocity of the partial streams of theceiling gas stream—uniformly since they are equally sized and arrangedat regular distances from each other on average. In the course of this,here, the holes 53 have a diameter of approximately 2.5 mm. In thecourse of this, the ratio of an area perforated by holes 53 to a totalprocess chamber ceiling area is approximately 3,8%.

FIG. 16 shows the perforated metal plate 52 of FIG. 15 in a built-instate in the ceiling 4 a of a process chamber 3 in a schematicperspective view inclined from below. In this example, four couplingwindows 35 a, 35 b, 35 c, and 35 d of a four-scanner-machine, which may,in particular, be an apparatus as in FIG. 2, are arranged in the processchamber ceiling 4 a within the inner opening 54. Centrally between thecoupling windows 35 a, 35 b, 35 c, and 35 d, a nozzle 43 is arranged,through which the central gas stream 40 (not shown) according to theinvention can stream into the process chamber 3.

FIG. 17 shows a process chamber 3 having a perforated metal plate 52 asin FIGS. 15 and 16 built-in in its ceiling 4 a, partly in a verticalcross-section, in a schematic perspective view inclined from above. Inthe course of this, in particular, it may be a process chamber 3 of thefour-scanner-machine 1 shown in FIG. 2. A gas supply pipe or,respectively, supply pipe 46 a ends in a central gas inlet, here in formof a nozzle 43, representing the gas supply device according to thefirst aspect of the invention. The process chamber ceiling 4 a liesabove a build area 10 and comprises a hollow space 73 having a wall.This hollow space wall comprises an outer wall region 74 turned awayfrom the process chamber 3 and an inner wall region bordering theprocess chamber 3, which is formed by the perforated metal plate or,respectively, the perforated plate 52. In a vertical wall section of theprocess chamber wall, an outlet 42 a or 42 b starts directly above theprocess chamber bottom 4 b or, respectively, a plane of the build area10, the outlet having two opening slits extending horizontally. Theoutlet 42 a or 42 b extends at a distance from an edge of the build area10 and parallel to a side of the build area 10 and extends in thisexemplary embodiment in its length beyond the side length of the buildarea 10 being parallel thereto, so that a removal of impurities inregions above the process chamber bottom 4 b which do not lie above thebuild area 10 is improved.

FIGS. 15 to 17 show that a process chamber ceiling 4 a does notnecessarily need to be plane-shaped and/or lie parallel to the buildarea 10 across the whole of its area. Vertically above the build area10, the process chamber ceiling 4 a shown here is substantially planeand lies parallel thereto, it, however, has a section 72 rising up awayfrom the process chamber bottom in a slant manner above a region of thebuild area edge.

This section 72 does not impair the functioning of the ceiling gasstream according to the invention, but is rather designed as the wholeinlet region of the process chamber ceiling 4 a such that, duringoperation, a homogeneous ceiling gas stream pours out from the openings53 into the process chamber 3 substantially vertically to the build area10. This is made possible by a defined control of a process gas volumewhich is pumped into the hollow space 73 of the process chamber ceiling4 a from the in this example two supply pipes (not to see in FIG. 17,arranged above the hexagonal areas 71 in FIG. 16) relatively to aprocess gas volume exiting the hollow space 73 through the holes 53 ofthe perforated plate 52 towards the process chamber 3. By a suitablesetting of parameters, such as e.g. a volume flow rate of the gas streaminto the hollow space 73 and/or a ratio of the areas of the openingcross-sections at in- and outlets of the hollow space 73, anoverpressure relatively to the ambient pressure in the process chamber 3can be generated during operation, preferably, in the whole region ofthe hollow space 73, which overpressure provides for a to a large extentequal velocity of the partial streams of the gas stream which streamthrough the holes 53 into the process chamber 3. In other words, a gasvolume introduced into the hollow space 73 does not stream further intothe process chamber on the shortest route through holes 53 of theperforated plate 52 lying close to the supply pipes, but rather firstlycontinuously floods the hollow space 73, so that after a short startingperiod, substantially in the whole hollow space 73 or, respectively,substantially at all openings 53 of the inner wall region 52 towards theprocess chamber 3, a substantially equal pressure, i.e. an overpressurerelatively to the process chamber pressure, prevails. Such anoverpressure can effect a homogeneous ceiling gas stream through theopenings 53 of the inner wall region or, respectively, perforated plate52 of the process chamber ceiling 4 a, e.g. in the present exemplaryembodiment of a process chamber ceiling 4 a having a big number ofopenings 53 of equal shape and equal opening area. In this case, thepartial streams of the ceiling gas stream have substantially equalvelocities and a substantially equal volume stream.

An influencing factor with regard to a target homogenisation of theceiling gas stream a hole size may be, i.e. an area and/or shape of anopening cross-section of the holes 53 in the inner wall region 52. At aconstant volume flow rate of a process gas which is introduced into thehollow space 73, a characteristic of the ceiling gas stream can bepurposefully changed by constructively simple means, e.g. by exchangingthe inner wall region 52 of the process chamber ceiling 4 a, forinstance, by a perforated plate having an irregular arrangement of theholes. Partial streams of the ceiling gas stream exiting theabove-described section 72 of the process chamber ceiling 4 a which isslant to the build area 10, firstly traversing the holes 53 at acorrespondingly acute angle to the build area 10, may be graduallyguided, again, into an approximately vertical direction to the buildarea 10 as they pass to the build area 10, as caused by further effects,e.g. suction effects of other regions of the ceiling gas stream or adeflection by a bordering vertical region of the process chamber wall,whereby in a lower region, e.g. a lower half, of the process chamber 3,again, a ceiling gas stream is produced which is substantiallyvertically directed to the build area 10.

Even though the present invention has been described on the basis of alaser sintering or laser melting apparatus, it is not limited to thelaser sintering or laser melting. It may be applied to arbitrary methodsfor generatively manufacturing a three-dimensional object by alayer-by-layer application and selective solidification of a buildingmaterial (preferably in powder form), independently of the manner inwhich the building material is being solidified. The selectivesolidification of the applied building material may be performed by anenergy supply of any suitable kind. Alternatively or additionally, itmay, for example, also be performed by 3D-printing, for instance byapplying an adhesive.

In the course of the selective solidification by an energy supply,energy may in general be supplied to the building material, forinstance, by electromagnetic radiation or particle radiation. In thecourse of this, the radiation has such an effect on the buildingmaterial in the respective region of a layer to be solidified that itchanges its aggregation state, undergoes a phase transition or anotherstructural change and, after a subsequent cooling down, is available ina solidified form. Preferably, the building material is a powder,wherein the radiation may, in particular, be a laser radiation. In thiscase, the radiation has such an effect on a region of the respectivelayer to be solidified that powder grains of the building material arepartially or completely melted in this region by the energy supplied bythe radiation and, after a cooling down, are interconnected forming asolid body.

A solidification device for the selective solidification by energysupply may, for instance, comprise one or more gas or solid state lasersor any other type of lasers, such as e.g. laser diodes, in particularVCSEL (Vertical Cavity Surface Emitting Laser) or VECSEL (VerticalExternal Cavity Surface Emitting Laser) or a row of these lasers.Generally, any device using which energy can be selectively applied to alayer of the build material as radiation may be used for the selectivesolidification. Instead of a laser, for instance, another light source,an electron beam, or any other energy or, respectively, radiation sourcemay be used which is suitable for solidifying the building material.Instead of deflecting a beam, also the selective solidification using amovable line irradiation device may be applied. The invention may alsobe applied to the selective mask sintering, where an extended lightsource and a mask are used, or to the High-Speed-Sintering (HSS), wherea material is selectively applied onto the building material whichmaterial enhances (absorption sintering) or reduces (inhibitionsintering) the absorption of radiation at the corresponding points andthen an irradiation is performed non-selectively in a large-area manneror using a movable line irradiation device.

In the context of the present invention, basically all kinds of buildingmaterial suitable for the generative manufacturing may be used, inparticular, plastics, metals, ceramics, respectively preferably inpowder form, sand, filled or mixed powders.

The invention claimed is:
 1. A method of generating a ceiling gas stream in a generative manufacturing of a three-dimensional object in a process chamber by a layer-by-layer application and selective solidification of a building material within a build area located in a process chamber bottom, the method comprising: providing the process chamber having a chamber wall with a process chamber ceiling lying above and extending over the build area; passing a ceiling gas stream of a process gas through the process chamber by streaming the ceiling gas stream from the process chamber ceiling towards the build area in a controlled manner; and supplying the ceiling gas stream to the process chamber through multiple ceiling inlets formed in the process chamber ceiling which are spaced apart and distributed over a region of the ceiling of the process chamber directly above the build area, with the ceiling gas stream out of the ceiling inlets combining from multiple ceiling inlet gas streams flowing from the inlets and directed to flow in a manner perpendicularly to the build area and therefore downwards onto the build area as the ceiling gas stream exits the ceiling inlets, the process chamber ceiling including at least one window for passing radiation used for the solidification of the building material into the process chamber; and the process chamber ceiling further having at least one central inlet in a section bordering on the at least one coupling window, the central inlet providing a central partial ceiling gas stream out therefrom towards the build area, the central partial ceiling gas stream shaped so as to widen in such a manner that the central partial ceiling gas stream converges at margins of the central partial ceiling gas stream towards adjacent inlet ceiling gas streams or overlaps with adjacent inlet ceiling gas streams at least in a lowest part of the process chamber above the build area, the ceiling gas stream and the central partial ceiling gas stream combining in a controlled manner towards the build area to generate a combined gas stream at least across the whole build area.
 2. The method according to claim 1, wherein the ceiling inlets are shaped and/or arranged and/or controlled such that the ceiling gas stream is homogeneously shaped in a lowest tenth of the process chamber height; and/or wherein the ceiling inlets are shaped and/or arranged and/or controlled such that the ceiling gas stream is homogeneously shaped in a plane of the build area and/or parallel above the build area, the plane extending at least across the area of the build area including a surrounding area of the build area or across a total area of the process chamber bottom.
 3. The method according to claim 1, wherein the process chamber bottom lies below the process chamber ceiling, and the build area extends over a partial region of the process chamber bottom, a distribution of the ceiling inlets at the process chamber ceiling is about the same in areas relative to a total area of the process chamber bottom, wherein the ceiling inlets are designed and/or arranged and/or controlled such that inlet ceiling streams of the ceiling gas stream are respectively directed perpendicularly to the build area downwards onto the process chamber bottom when the inlet ceiling streams exit the ceiling inlets.
 4. The method according to claim 1, wherein the ceiling gas stream is passed through the process chamber before and/or during and/or after the selective solidification of the building material.
 5. The method according to claim 1, wherein the process chamber ceiling further comprises a hollow space having a wall that is closed in an outer wall region facing away from the process chamber and that possesses ceiling inlets in an inner wall region bordering the process chamber.
 6. The method according to claim 5, wherein the inner wall region comprises a plate or the ceiling inlets are at least partly formed by holes of the plate so as to form a perforated plate; wherein the plate or the perforated plate has at least 10 holes; and/or wherein an average opening cross-section area of the holes does not exceed 10 cm²; and/or wherein a sum of the opening cross-section areas of the holes does not exceed 20% of a total area of the process chamber bottom.
 7. The method according to claim 1, wherein at least one of the ceiling inlets and/or at least one additional gas inlet into the process chamber is designed and/or controlled such that, depending on a spatial configuration of the process chamber and/or on a position and/or size of a device arranged inside the process chamber, a velocity and/or an orientation and/or a jet cross-section of a partial ceiling gas stream streaming out of the ceiling inlet or the additional gas inlet are varied prior to and/or during and/or after the object manufacturing.
 8. The method according to claim 1, wherein prior to and/or during and/or after the manufacturing of the object, a process gas is supplied to the process chamber in a closed process gas circuit and is discharged from the process chamber through an outlet; wherein the ceiling gas stream represents at least a part of the process gas circuit; and wherein supply and/or discharge pipes of the process gas circuit include a conveying unit that varies a velocity and/or velocity distribution and/or pressure distribution of a total process gas stream or of the ceiling gas stream in the process chamber prior to and/or during and/or after the manufacturing of the object.
 9. The method of claim 8, wherein the process gas circuit further comprises at least one of the following gas streams that removes impurities generated during the solidification of the building material from the process chamber: a central gas stream that flows into the process chamber prior to and/or during and/or after the manufacturing of the object through a central inlet formed in the process chamber ceiling and flows out of the process chamber through at least one outlet, the central gas stream impinging within a central region of the build area at an angle of at least 45° to the build area; a lateral gas stream that flows into the process chamber prior to and/or during and/or after the manufacturing of the object through a side inlet arranged at a build area side and flows out of the process chamber through at least one outlet arranged at an opposite side of the build area.
 10. The method according to claim 8, wherein a ratio of a total inlet opening area to a total outlet opening area of the process gas circuit is varied prior to and/or during and/or after the manufacturing of the object, whereby, a velocity and/or a pressure of the process gas is/are varied at least in a partial region of the process chamber.
 11. A control unit for an apparatus for generatively manufacturing a three-dimensional object, wherein the control unit is designed for generating control commands for the automatic execution of a method according to claim
 1. 12. An apparatus designed and/or controlled to automatically execute the method according to claim
 1. 13. The method according to claim 1, wherein the ceiling inlets are uniformly distributed over a total region of the process chamber ceiling except for a coupling window region occupied by the at least one coupling window. 